I find my supply decreases by the end of the week as well, so you're not alone. I drink plenty of water, gets lots of sleep, and am drowning in oatmeal. By the time Friday comes, my body is just ready to be done pumping. I pump 3x a day at work right now and nurse at home. I have plenty of milk while nursing at home but that last pump session on Friday afternoon at work always freaks me out that my milk supply has dried up suddenly. But as soon as I get home and baby can nurse for an hour I know I'm okay. Hopefully your milk evens out soon and you can pump a steady supply all week. I've been pumping for 9+ months and mine hasn't, but maybe yours will!
From my iPhone, probably while BF'ing.