Mucosal pigmentation. Is it treatable?

Since 2 months i have been facing pigmentation of my buccal mucosa, initially it started in the right side but now it has started on left side too, also i have seen similar lesion below top lip as well. I have checked it physically by a dental surgeon, and ent, they're saying its physiological pigmentation and nothing to worry about but thing is i am getting worried as its kinda increasing in size, no tenderness though. I am not a smoker or tobacco user as well! Also i had been prescribed kenacort, caziq, dologel in past which did nothing but reduce the symptoms temporarily.. i am really worried :(. Also the only symptom is when sleep and the teeth rubs to that place, it feels a little rough. I want to exactly know why is it happening and is it treatable? I am worried because I don't want it to turn into some kind of cancer :(. Please help me sir/Ma'am