My baby boy has just gone on 5 mths old and recently whilst changing his diaper I discovered he has a small hole above his bottom hole. It has obviously always been there but because he was so small we obviously didn't see it!he was conceived naturally,and there were no complications during my pregnancy but he was born prematurely at 35 weeks...even though he was early he was a healthy birthweight,and had no issues requiring specialist treatment!please explain what this might be and what we should do about it!?!