My 3 year old male has a recurring sore on his lower lip. . The area will heal up then crack open...does this repeatedly. No bleeding just looks a bit red in 2 or 3 places always in the same area. This has been going on for many months. He has been seen by the vet. We had it biopsied and the test was negative for any cancer. He wanted us to try an oral antibiotic and that did clear it up but then it happened again. And on its own it will heal up for several days only to crack again. Any ideas or suggestions? Something more I can ask the vet to do or check or???