How to get better at chess?

Have you read an endgame, middlegame, opening, tactics, and annotated game collection book? Do you play in OTB tournaments often? Do you analyze your games? Do you have a coach? Do you practice a few hours a day? Have you given up or very much limited speed games in comparison to all other chess related activities?

It's a matter of time. "playing for weeks" is just a drop in the ocean. Chess is a tough game to learn to any proficiency (more so if you are an adult). Think in terms of three to five years to reach something like your final strength.
I think tactics trainer ratings are generally higher than standard ratings. I know that is the case for me anyway. Don't read too much into yuor chess mentor rating.

study your games and find out where you went wrong,try to figure it out first without help of computer,you dont need to be too deep just try to find reasons behind your losses and avoid them.for example if u played opening very bad,learn that opening and have some clue about subtleties so you dont repeat the same mistake again.