we have had HUGE problems with this issue, DS was almost completely day TT, then he had a bad reaction to some antibiotics and stopped pooing
I tried everything natural I could think of, prunes, juice, apricots, pears etc, etc...
Giving fibre can actually make it worse.
its a tricky thing as just one hard to poo moment will trigger the fear, then they hold on again for too long and it hurts the next tie and the cycle continues.
I received some fantastic advice from here on this forum, I went to see the GP and explained what I I thought was going on, what research I had done, and how I thought best to treat it, he was amazed and just basically told me it would be fine and to go ahead. we started using parachoc, everyday, for about 3 months, until he would again go to the loo with no complaints (I have had him screaming in hysterics at doing poos, doing them in the bath, doing the "poo dance" until he couldn't hold it in anymore, its heart breaking!)
We have had a few regressions (hospital stays, operations etc... it all went down hill!)but we are now almost on the other side again.