I have a purplish colored sore on my uvula and it is sore. what could this be?

Petechiae: Sometimes, viral or bacterial infections can cause an area of bleeding below the surface of the mucous membrane. The medical term for that bleeding is petechiae and is probably what you have. If it is present for longer than a week or is so sore you can't swallow, you should see a doctor.

Cold sore?: If this sore is terribly painful to the point that you can hardly swallow, it could be a herpes lesion, or cold sore. These can occur anywhere in the mouth and can be very uncomfortable, to the point that it is hard to eat and drink. If that's the case, you could take Valtrex (valacyclovir) during times you have a herpes outbreak canker sore.