Losing focus :c

Good day fine sirs,

To introduce myself, I am a platinum Zerg, who just now switched to Terran and is starting to actively Ladder again.

But I am facing a problem I have been facing my whole Starcraft "carrer" As the Game goes longer, i just loose focus, up to about Minute 12-15 or something like that, I am playing my best, but as the Game goes longer, I just loose focus. 

I know that the longer the Game goes, the more stuff I have to do, but still, I sometimes for some reason just forget about my Game Plan, about Scouting and everything :c

Are you facing this issue too? Have you been facing it and solved it? if yes, how? Or is this just something personal? Maybe just playing tons of practice Games is the solution? 

I hope you guys can help me, Cheers!

Jonas aka NTSFreibier