Baby stays constipated..

My daughter will be 9 months soon..I breastfed her until 3 months then used the similac supplement formula and then started the sensitive and also the gentlease formula. Ever since I started the other formulas she’s stayed constipated. She’s been on sensitive but I recently tried the gentlease and it didn’t change anything. I was wondering if it would be ok if I tried the supplement formula again to see if it would help her? She tries so hard to poop but only a tiny bit will come out in about 3 diapers before finally at the end of the day she gets the rest out. I’ve been having to take her to the changing table and push her legs up when I know shes trying to poop and help her get it out or else it takes her all day to get it out. And it hurts her too. I was trying to feed her more fruits but she doesn’t like the baby food and doesn’t really eat a whole lot of table food. I’ve been putting an ounce of prune/apple juice in her morning bottles to try and help but it only really helps if I push her legs back every time. 😔