Baby girl backed up..

Jennifer

So i recently had my gallbladder removed while I was hospital i pump and sent it home and formula as well.. now that im feeling better .. ive seen my daughter more irritated and jusy not being herself I think she is contispated or back up.. what can I buy or give her too poop. She will be 4 months in october 6. Please help

She never cries and becomes irritated.