Suddenly scared to poop

BoSoxbride

We successfully did the 3DPT a couple weeks ago, and he pooped just fine on the potty then. But for the past week he's been holding it. He had one incident where he pooped his pants, and was very upset. And then he almost made it to the potty on another occasion (after  not having pooped for 3 days). We've been giving him PediaLax chewables on occasion to try and encourage it, but he's just so scared. He walks around crying and asking us to carry him (because his belly hurts). Today we got him to sit several times trying to poop, but I think he's constipated at this point.

Any suggestions on dealing with the pooping fear, would be appreciated. TIA