Bearded dragon lip discoloration and swelling

I noticed a spot along my bearded dragons lip last week that was hard and appeared to be swollen a little. It was black on the surface. I thought it was mouth rot. This happened before and I took him to vet and he prescribed neo/poly/DeX drops to apply two drops on area every 12 hrs. I didn't do any research on the mouth rot or medication before. On yesterday I researched both finding out that mouth rot Is within the mouth and that the medication is used to treat eye problems. I am now wondering why this was prescribed and what that issue really is about on his lip that has come back a second time. The doctor said it was mouth rot. I will be checking his teeth this morning. Should I continue with that medication or should I do something different, can anyone help? It went away then an it clearing on the lip. I'm just concerned on giving medication that goes in eye to an area of his mouth

Please post a pic of the lip
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Karrie

Hi everyone sorry I didn't get back sooner. I gave him a bath and it came off with shed on lips. I had been giving him the medication for about 12 days and it did help. I took him to emergency and they said he didn't have mouth rot. She said medication did work and that he looked great. I was very relived, this is my best buddy. I want the best life for him. Thanks for all your concerns and help?