Even masters suffer the same fate, Jimmy. I wouldn't feel bad.
First of all, don't relax too much. You have to force your mind into jet mode. You have to search that board like the DEA messing things up, and you have to put out a lot of effort when calculating your variations. Effort! Effort! Effort! You only rest when the match is over.
Second, brush up on your positional assessments. Sometimes you simply don't have the time to explore a move for too long a period. You need to be able to assess whether you're still going to benefit from the move whether it's the best or least candidate. You can only do this effectively by understanding positional play... and tactics.
I play half hour games-not online. I'm always in time trouble. I try to be disciplined, go through a checklist each move--what's the threat, check for checks, etc...-- but I have to abandon that approach as time winds down. Any advice on managing time better?