I have a sore in my mouth, looks like a little line of yellow. it's by my gums but on the upper part of my cheek, doesn't hurt but keeps coming back?

Need exam and: possible biopsy. See ENT or U can start with PCP or dentist. Good luck

Sore in mouth: generally recurrent sores in the mouth are from Herpes simplex virus -A. Most of those are however, painful or at least uncomfortable. There are many other causes. First see your dentist and if cleared get to your family physician. If viral in nature, you may need a suppression therapy.