baby formula constipation?!

Sydney • Mommy to Roxanne Everly Mayers, born Christmas Day 2016, 8lbs 2oz bundle of beauty. 💛 step mom to Ryko Yancy ❤❤
So my 3 week old daughter was originally breastfed but I ended up in the hospital with bad mastitis and an abscess and haven't been able to produce since then. I had to switch her to formula, which I get on WIC, so I'm only allowed to get similac advanced. If I could afford any myself I would explore other options. Anyways, she hasn't pooped in almost two days and it was to the point that she was obviously uncomfortable, so I gave her about 3/4ths of a pedialax suppository. That worked but seemed to be pretty hard on her stomach, so for future reference, is there anything else I can do?? Please help!