I find it difficult to open my mouth fully as my cheek seems raw next to my upper row of teeth. i can't see at the back of my mouth as my cheek is swollen?

Back of mouth issue: Cheek swelling and mouth pain needs to be explained. This likely involves infection or inflammation in teeth toward the back of mouth, the cheek tissue itself (cellulitis), the gums (gingivitis), or a tooth abscess, among other possibilities. I would check with your dentist or an oral surgeon.

Raw cheek: Can be from tooth infection, gum infection, and/or cheek infection. May also be a joint problem. No magic bullet. You've got to see a Dentist, someone who can physically examine you, run the appropriate tests, do the appropriate imaging, and arrive at the proper treatment plan based on the diagnostic findings. Please don't put this off.