Hun, I have a friend who went through this with her DS at a similar age. They had one bad bowel episode, and afterwards he regressed to pooing in his pants. It turned out that he was just way too scared to go to the toilet, it just hurt too much. She kept seeing Drs until someone listened to her and helped her to sort out the problem. Which was not that he was being naughty, but that he was having real problems with his bowels. As well as other things, time, patience and understanding helped him to get back on the toilet. He was fine within months .

It is probably worthwhile going back to see an understanding Dr for more advice