A cavity in a tooth may not hurt for several reasons. It may still be very small (which is the best time to find them and fix them), it may be quite large and filled full of soft fluffy decayed tooth material which may act as an insulator from cold or hot, or the nerve of the tooth may have died (which will result in an abscess and/or the loss of the tooth). If a cavity exists, it will not heal by itself. Get it fixed as soon as possible.

If your tooth hurts all the time and you have a fever, this is very serious! If your toothache is present all the time or if you feel stabbing pain even when you aren't eating or drinking, your tooth is most likely infected.