Whole milk constipating 12 month

Crystal

It’s been about 3 weeks since we’ve switched to whole milk and she is so constipated nothing works. Tried prune juice apple juice water, definitely switched and gave her more fiber foods that she would eat . we’ve been in and out of the doctors office because she cannot pass her stool. She was prescribed miralax but it doesn’t even seem to help her as much. Any advice???? Tired of seeing her cry in pain because she can’t pass her stool