Burning/ stinging red spot appeared on leg all of a sudden. the skin is peeling off and its moist when i touch it. what could it be?

Drug reaction?: It's very hard to say without more information. But if you're taking any medications, and especially if you started a new drug recently, this sounds typical for a fixed drug eruption. FDEs are sharply localized rashes due to drug allergy. The appearance is often much like a burn, which seems to fit with your description. Some drugs are especially likely to cause it, including certain antibiotics.

Insect bite: insect vs contact dermatitis. advise to see dermatologist if continues to enlarge or other symptoms develop. Once in awhile, these lesions can become infected