Supply question?

Amberrrr

So I started going back to school twice a week. I go from 6-9:30, on Tuesdays and Thursdays.. It seems that my supply has dropped a bit from about that time every day. I still produce enough milk to feed LO but not enough to pump more than an ounce. Any other time I get 2-3 ounces during a pumping session. During my night feeding sessions I find myself feeling pretty engorged!  Could it be that going to school even for those two nights a week is messing with my supply during those hours? Or could it be something else??