I have a pea-sized painless red bump in my throat on the right side. tonsillectomy at age 10, 18 now. could my tonsil be growing back?

Not growing back: Tonsil tissue is composed of lymph tissue, similar to a lymph node. The back of the throat, the tongue, and the tonsils all contain lymph tissue. When a tonsillectomy is performed the tonsils are separated from muscle. The bump you are identifying is likely a little bit of leftover tonsil tissue. This won't cause you any trouble.