My DD went through this except poor thing ended up pretty constipated...
I was told- apples soak up water so not recommended to have too many apples.
Iron can cause constipation as well.
Pears are good and water.
I tried prune juice and i boiled prunes to put into cereal but no success... what worked for my dd was a weak cammomile tea. No one recommends this but i couldnt find any real reason why its not recommended and mum brought me and my brother up on this so i gave it a go and it worked. She has it about once a week now. I make it with a tea bag for a litre of water and dont leave the tea bag in too long. My pead didnt say anything when i told him i have been giving it to her so im not sure.. maybe if someone knows something about cammomile that i dont before u try it.. Good luck.