Baby belly ache?

My daughter is breast and formula fed this is what her pediatrician said to do and the pediatrician for the nicu before we were released. Now when she poops or it comes around the time she normally poops everyday she makes it seem like it hurts to poop or it takes her a lot of work to get it out. Is there anything I can do for her? We’re going to the doctor this week on Thursday and I’ll be asking her doctor then.