Constipated baby! please help!?

My 2 month old baby is very constipated, we took him to the doctor on tuesday and they put him in prune juice and glycerin suppositories, he was pooping with the glycerin suppositories but they seem not to be working on him anymore plus he got a really bad diaper rash wish I think its cuz of the prune juice, my baby is in s much pain and I just can't stop crying with him. What do you think should I do? If u have any experience like that please tell me thank you!