Without seeing it, I would say it "sounds" like time for a new one. Are there strands broke? If yes, change it. If no, try to wax it and see how many shots it takes to start fraying badly again.

Also, what kind of string do you have on there? There are other reason/benefits to changing your string. A good after market string can get you some extra fps, as well as not having as many twisting/stretching issues that most stock strings have.