I have a sore at the back of my mouth by my gum, is there any medication i could use?

Mouth sore: This is most likely a canker sore. Apply ice chips periodically. I have recommended bathing the sore with maalox several times a day. Other suggestions include tea bags or tea rinses. Physicians can prescribe cortisone type pastes or lidocaine topically.

Sore: What kind of "sore?" Raised, indented, erosive, traumatic, red, white, tender, swollen, smooth, size, borders, duration, and so many other questions? Treatment should be based on diagnosis. You need to be examined to determine cause. Once diagnosed used, appropriate treatment can be ordered. Sore could be draining tooth abscess, viral infection, neoplasm, etc. See a Dentist NOW.