Talk to Ent Specialist on Mouth Blister

i have mouth blister problem since 3 months its only one blister at same spot comes after every 3 days interval it appears, swells, pops heals in only one day then leaves only minor mark then reappears after 3 days its size is about 4mm with no pain at all but when it pops minor blood comes then it heals itself in one day its watery round shaped crystal transparant blister inside mouth just back of daar ( the big teeth of right down corner) i am facing this issue since 3 months i hve visited an ent specialist he checkd and said nthing to be worried and prescribed exlant capsaul for 15 days i tried it but didnt work i viaited 2 more doctores 1 said use somogel and folic acid and besefol, i tried it but didnt work 2nd docotr said use polymalt and oral drop nelsalt i tried but didnt work, please doctors help me.