I'm on amoxicillin for cold but have abscessed tooth for over a month. how long should i wait before treating the tooth?

Not long: Abscessed teeth are nothing to play around with. The infection can progress from the tooth into the soft tissues around the tooth pretty quickly in some people. See your dentist and get it taken care of.

Don't Wait: Something's not right...Amoxicillin is not indicated for the treatment of a cold. You shouldn't be taking that. Furthermore, an infected tooth will never heal itself, even if the pain and swelling eventually get better. You should have the tooth treated immediately. A month is already far too long. How long would you wait to treat an infection anywhere else in your body? Not that long, i hope.