An ingrown nail is not necessarily obvious. Dig in there and be sure it's not growing into the skin unless you can see it.

It might be an infection. A doctor can give you the best advice for this but if it is then there's an over the counter anti-fungal called Lotrimin that's effective. If there's an infection back under the nail you'll need a prescription.

I'd get it looked at if you don't see the problem.