DS is nearly 3 months old. Every poo he does (and he does a lot) travels in a backwards and upwards direction, so it frequently leaks up the back of his nappy. It's even more of a problem if he's in the sling (which is a lot of the time). I've tried going up a size, but it just moved the poo leak from the back to the leg. He's currently in ASDA little angels nappies and they don't really seem to absorb poo at all. Is this a size problem or a nappy type problem? What should I change to reduce the risk of poo leak?