T.C.
We had the same, if not close to the same problem with our 4 year old daughter. Turns out she was anemic because she won't eat veggies. Once we get got her iron levels up with iron drops and a multivitamin w/iron and making the deal that she eats one mouthful of veggies everynight (or she gets the YUCKY iron drops) she goes like a pro. It was virtually in like 3 days that she started going and going well.
We went through the enimas, laxatives, suppositories, everything to get her back on track with going poop..those worked at times..now that her iron is normal so is the pooping.