We have the same problem with our almost 2 year old. She isnt a big eater, but I have increased veggies and fruits, but to no avail. 

Her bowel movements are what we refer to as "rabbit pellets". About every 3 days I give her a glycerin suppository, which seems to get things going.  Her Endo doesnt seem to think it is related to CAH..........who knows. She is SVCAH and doesnt have any urinary tract problems.