I was stung by a wasp thur. The redness and swelling went away fast. It got red and swollen yesterday and now itches and is hot. Is this normal?

Not unexpected. The venom of insect often sensitizes people so that most end up becoming allergic to it. Your initial response was to the chemicals present in the venom and the late response was likely from the allergic response to it. Try antihistamine and topical cortisone.