What To For My Kids Constipation Problem?

hi, my 2 1/2 year old has been constipated for a while now. We have been giving her laxatives (on dr orders) and it helps some but it is still a constant problem. Yesterday she passed a small, white, gummy looking stool. We thought it might have just been some gum she swallowed a while ago. When i changed her diaper this morning though, she had a large, hard stool that was slightly covered/intertwined with a little more of the white poop. It was almost chalky. Should i be concerned? Is this just because she hadbeen backed up for a couple days? thanks.