Belly button picking/playing?

My son is 15 months and won’t stop picking or playing with his belly button, it’s so red and looks sore.

I’ve been trying to keep onesies and sleepers on him, as well as keeping his nails trimmed, but he still plays with it and so it won’t heal. I have been putting polysporin on it every night, and every morning, sometimes during the day if I can remember.

I dry it really well after bath. Is this normal for babies to do, or should I be worried that he’s doing it because it’s bothering him? When I clean it or put polysporin on it he doesn’t seem bothered by it at all.

Any insight or advice on how to help it heal would be great! :)