How Can Chronic Constipation In A Toddler Be Treated?

Hi. My little girl often has stomach problems and can not poop. Sometimes I give her pedialax. It is a chewable that helps my two year old when badly constipated. My husband and I usually tell the other if we are the one to change a poop diaper so we know, however, this morning after her bath, I gave her TWO pedia. Lax to find out that she had gone already before her bath. So I gave her two for no reason and she has been miserable most of the day. I got her to eat a few grapes, half a ham sandwich, a bit of cheese, and some peanut butter. She has drank a wee bit of rice milk and two bottles of water. This morning she had a bottle of Juice. She does not want anymore food and it was slow getting her to accept and eat some of the others. What do I do?