Sounds like a little infection. First, dry your belly button - if it's a little deep, try a Q tip gently to absorb the moisture. Getting the moisture out will help the skin be less vulnerable. It is either a yeast infection or the other thing that lives on our skin, bacteria. It won't hurt to put some clotrimazole on it. If it is yeast, as you already have seen, the redness will go away in a short time. If it is bacteria however, the clotrimazole won't help at all and I would put an antibiotic ointment (bacitracin, or neosporin, etc) on the skin. If it is a bacterial infection, the clotrimazole might make it a bit worse because it will kill any yeast around and that makes the bacteria happy - they kind of compete for a life on our skin. So, if the clotrimazole makes it worse, go right to the antibiotic. Just like the infection you have had under the skin fold before, you should be able to clear this up at home. If it just spreads onto your abdomen you'd want to have it checked but that is not likely.