My fixed tooth hurts, what's the solution for the pain?

Root canal?: The solution depends on the problem. If by fixed you mean it was filled then the cavity may have been too deep and now the pulp of your tooth is irreversibly inflamed. This situation is solved by doing a root canal on the tooth the remove the infected pulp. There may be other solutions but your question needs to be more specific. You can try 800 mg of Ibuprofen every 6 hours or 2 alleve every 12.

Depends: If you are temperature or biting sensitive. It is probably a root canal problem. Sharp pains mean a crack. Throbbing pain may be a gum problem. So, see your dentist, asap!

Not good: Not a good sign if beyond a week after treatment. See dentist, a root canal may be necessary.