Sore bum and genital area

Ok vets and vet techs, I have a question that i hope you can assist me with. I have a 10 weeks old kitten. He was fine and then had yellow poop, maybe from the food but with his lack of energy we assumed it was a sign of infection. I got the poop where its brown now with antibiotics, between the more solid shaped poops he leaks some. Hes eating really well, have him on a fiber based vitamin and nutrient food as well as nutrigel to hopefully get his runs more solid. His belly is round even after deworming as his sister had tapeworms. We figured this was also playing a part in his illness. I can easily feel the hip bone but hes drinking alot. I got him on plain clear pedialyte added to his water and added a little to his food so it's more gruel texture. He knows how to clean himself but sometimes he doesnt. And his bum is sore. I'm working on stopping the leaking between bowels so that he doesnt dehydrate. With him cleaning himself, I'm not sure how to soothe his bum so if he licks it, it's not bad for him??? Any suggestions? I'm trying to get him to gain the extra fat on his hips as well as keep him hydrated but the sore bum I'm stuck on.

Want to also add, due to switching him to can and adding a little pedialyte, hes not drinking as much straight water. He only seems to leak when he has to poop now but it just oozes out and then when he uses the litter box it's more solid but soft and no signs of worms whatsoever. His poop is more Like toothpaste when he does use the box. So I'm not sure how to completely control that.

Hello!  So let me clarify:  your cat has soft poops (yellow for a while, now returning to brown), is underweight and drinking a lot, and has had some antibiotics (but not from a vet?  I trust you are not in the UK, where we are based- that would be illegal here).  They are also eating a lot of fibre. It's worth remembering that cats are carnivores, not really designed to eat or digest substantial amounts of fibre.  Either this, or the antibiotics (I am going to assume for the moment that these were species and dose - appropriate), could actually cause runny faeces, sore bottom and large tummy in itself.  However, there is a long list of other problems that could also be involved here. Furthermore, there is only so much fluid that a kitten can lose before they become dehydrated and seriously ill.  The reason for their extreme water-drinking may be to do with dehydration, or they may be managing to keep up with the fluid-loss in the faeces by drinking so much.  It is hard to tell from here.  Please see a vet as soon as possible to get them checked and, if nothing else, to advise you a good, kitten-appropriate food for your cat.

It is best to buy food especially formulated kittens, which will contain the correct proportions of nutrients to help them to grow.  However, what with being underweight, drinking too much and the skin around the anus possible needing attention (it should be sensitively cleaned and perhaps a protective cream may be needed), a vet should be consulted at this point.  Best of luck and we would love to hear how you get on.