Working moms...

Has anyone just gotten increasingly sad after having to go back to work? I was lucky and got 16 weeks of leave... But still, I'm so guilty about being gone and I miss him so much. I struggle to produce breastmilk with a pump, so I only can get two 3-4oz bottles to bring home after pumping 3x during the day. My stash is already almost gone after just 2 weeks in... He has to have a bit of formula during the day too so he doesn't go hungry. Just so sad and depressed. Any tips for getting through this???