Losing in silver due to micro. Really! Help!

Hey! I'm a terran silver player on a losing streak. The thing that annoys me the most is the fact that I lose tons of games where I'm really ahead. Like, the graph at the end of the match puts me above my oponent most of the game when, all of a sudden, it plummets.

It seems to me that I don't know how to engage. I lose 90% of TvT that get past the 8 minute mark regardless of my macro. When my opponent manages to build half a decent siege line, I'm done. Zerg usually depends on the number of banelings, with protoss being my best matchup.

I'm trying to go simple: 4-rax TvT and TvZ and 3-rax TvP, but I don't think I'm getting better. Any advice? Thanks!