I just can't get better I hover around the same rating constantly and I don't know why.
its ok, as you increase in where you are strongest, you will naturally get stronger everywhere (even if you do not play much of it!).
For instance, my friend used to play and grind a huge amount of bullet and reached 1800. I however had never played a single bullet game then for nearly 2 years and my bullet elo was 900 because I hadn't played bullet against other people than friends (and sometimes the challenge would be rated accidentally).
I played my friend in 5 games, and won all of them. Reason was that my rapid rating was 2000 - 2100 while theirs was 1800.
I just can't get better I hover around the same rating constantly and I don't know why.