My gums (left side) at the very back of my mouth hurt. (bhind last molar) wisdom teeth pulled years ago. what else may be causing this irritation?

Maybe gingivitis: The gums behind the last molars can get inflamed, called gingivitis. That area is harder to keep clean with brushing and flossing, so gingivitis happens more often. A dental cleaning can help. Meanwhile, brushing vigorously to clean out that area, and then being very gentle with that area for a week, may let it heal up. If discomfort remains, a dentist can check if it is something bad like cancer.

Many things: It could be food impaction behind the tooth and gum tissue. Or tooth decay which is leading to a draining abscess. It could also be periodontal disease causing a pocket which traps bacteria and food debris causing a periodontal abscess. It could be any number of things, and the only way to really find out is by getting a dental exam with xrays.

Sore gums: The most remote cause may be a small splinter of bone from the wisdom tooth that is floating out of the gums. You may have an ulceration or sore like a canker sore or herpes' lesion attacking that location making your left jaw painful and difficulty swallowing. Also, the gums can get a local infection surrounding the tooth. Most of these will heal within a week.