Similac pro sensitive

My baby is a bit lactose intolerant so they told me to give him similac pro sensitive everything was fine but now it’s making him extremely constipated and when he does poop it’s extremely painful for him. Does anyone know a different formula like pro sensitive?

** I was exclusively breastfeeding then my supply started to drop so I had to start supplementing. I got sick a couple weeks ago and my supply completely suffered. Now he's pretty much all formula. Idk if that matters