My thumb is very swollen & feels very warm. I can't bend it. I also have a thumb ring on that I can't get off. What is it & what should I do?

First . First get the ring off. Soap or lotion may help. If one cannot remove it, a ring cutter or a tin snips may work. In any case a swollen warm thumb can be a sign of infection. An infection can be mild, made to look worse from a tight ring, or it can represent a severe infection known as flexor tenosynovitis which needs antibiotics and quite possibly surgery in a timely emergent fashion. There are many different types of infection that can occur in a hand or finger and the important thing is not to allow it to rapidly worsen ( see link for hand infections below) other causes can be trauma, gout, a trigger digit ( where the thumb flexor tendon is locking--see link below) and various forms of arthitis. You should seek medical attention. Most emergent care areas have a ring cutter. No matter what the cause, the ring makes things worse, get it off of have it removed.And get seen by a medical provider.