Since you posted no games to analyze i have no idea what the issue is.
Software to analyze my my opening mistakes.

What openings do u use as black? computers only show your tactical mistakes. If you lack understanding of basic opening principles computers won't help you.

If I were in your shoes, I'd probably just download a copy of Scid vs. PC, open your games database, and use a combination of the Tree Window and an analysis engine. There might be more elegant solutions, but Scid vs. PC should be good enough. [Edit - Oh, you'd also probably want to filter your database and create two smaller databases; One database with all of your White games, and another database with your Black games.]
http://scidvspc.sourceforge.net/index.html

What openings do u use as black? computers only show your tactical mistakes. If you lack understanding of basic opening principles computers won't help you.
(I believe) I have idea of opening principles, at least I read ~3 book about that. It does seem like I'm just missing some traps over and over again (but I may be wrong).
I don't have any openings memorized actually. Most of the times it's 1. e4 e5 2. Nf3 Nc6, and after that I know no variants, just "opening principles".
Because general consensus is that novice players don't have to memorize openings, they just need to know principles in the beginning and focus on other parts of the game (tactics and endgames, for example).

If I were in your shoes, I'd probably just download a copy of Scid vs. PC, open your games database, and use a combination of the Tree Window and an analysis engine. There might be more elegant solutions, but Scid vs. PC should be good enough. [Edit - Oh, you'd also probably want to filter your database and create two smaller databases; One database with all of your White games, and another database with your Black games.]
Thanks for the suggestion, will try that.
I tried "chess position trainer" yesterday, but it seems that I'll need to read the manual to understand how to use it. And also UI was a bit slow.

Lucas Chess works 4 me! It has very good analysis features. Better than SCID vs PC IMHO.
I agree that Lucas Chess (LC) has better analysis features than ScidvsPC. LC would be a benefit when analyzing individual games. However, afaik LC doesn't have any kind of database tree view feature, does it?

What openings do u use as black? computers only show your tactical mistakes. If you lack understanding of basic opening principles computers won't help you.
(I believe) I have idea of opening principles, at least I read ~3 book about that. It does seem like I'm just missing some traps over and over again (but I may be wrong).
I don't have any openings memorized actually. Most of the times it's 1. e4 e5 2. Nf3 Nc6, and after that I know no variants, just "opening principles".
Because general consensus is that novice players don't have to memorize openings, they just need to know principles in the beginning and focus on other parts of the game (tactics and endgames, for example).

It is most likely tactical mistakes rather than opening understanding that is the problem. While solving tactical puzzles will help, this won't improve things much if you aren't looking for tactics or threats from your opponent.

What openings do u use as black? computers only show your tactical mistakes. If you lack understanding of basic opening principles computers won't help you.
(I believe) I have idea of opening principles, at least I read ~3 book about that. It does seem like I'm just missing some traps over and over again (but I may be wrong).
I don't have any openings memorized actually. Most of the times it's 1. e4 e5 2. Nf3 Nc6, and after that I know no variants, just "opening principles".
Because general consensus is that novice players don't have to memorize openings, they just need to know principles in the beginning and focus on other parts of the game (tactics and endgames, for example).
Post some games...

computers only show your tactical mistakes.

I'm a novice player (~1600 standard and ~1050 blitz rating on fics) and looking at my stats I can see that I win 75% of games as white while lose 70% of games as black.
I suspect that's because of some systematic mistakes that I make in openings while playing black (basically keeping on making the same bad move in the same position falling into some kind of trap).
Is there any service/software to which I can upload PGNs of my ~150 games and it will find such systematic mistakes?
I think it's early for me to memorize opening variations, but bringing obvious mistakes into my attention would be useful I think.
You can download chessbase light

As 1.e4 is opponent's move when I play black, I don't have much choice on that move.
(Or if you meant not playing 1.e4 as white) I believe that the advice usually given to novice players is to "always play 1.e4 as white at first, and only switch to other openings only when you gain enough skills", while you suggest replacing 1.e4 with something simpler. What would you recommend that is simpler than 1. e4?

As 1.e4 is opponent's move when I play black, I don't have much choice on that move.
(Or if you meant not playing 1.e4 as white) I believe that the advice usually given to novice players is to "always play 1.e4 as white at first, and only switch to other openings only when you gain enough skills", while you suggest replacing 1.e4 with something simpler. What would you recommend that is simpler than 1. e4?

As 1.e4 is opponent's move when I play black, I don't have much choice on that move.
(Or if you meant not playing 1.e4 as white) I believe that the advice usually given to novice players is to "always play 1.e4 as white at first, and only switch to other openings only when you gain enough skills", while you suggest replacing 1.e4 with something simpler. What would you recommend that is simpler than 1. e4?

You might want to read over some of Heisman's Novice Nook articles regarding openings (Section 8). There are some good ideas in those articles.
https://web.archive.org/web/20151004234008/http://home.comcast.net/~danheisman/Articles/subject.htm
I'm a novice player (~1600 standard and ~1050 blitz rating on fics) and looking at my stats I can see that I win 75% of games as white while lose 70% of games as black.
I suspect that's because of some systematic mistakes that I make in openings while playing black (basically keeping on making the same bad move in the same position falling into some kind of trap).
Is there any service/software to which I can upload PGNs of my ~150 games and it will find such systematic mistakes?
I think it's early for me to memorize opening variations, but bringing obvious mistakes into my attention would be useful I think.