I had a problem with Oskar about 6ish months ago holding it in cos he didn't want to poo on the toilet or really in a nappy... and he was holding it, like you we could tell. Doc said it's called anal retentive... lol true! He told me to get Lactulose (which is a laxative) and just give 2.5ml (which is really small dose) once a day but I think he only had it 2 times? The thing is it might be hurting cos he's constipated so holding and the problem with that is apparently if not careful cos it gets big and hard they can tear their bottoms and it can be rather nasty. So that is why he told me to use the Lactulose. I've never had to use it again, it just softened it up rather than made him go so it made it easier. Try also to keep up water.