I have pain in the top of my jaw and i can't close my teeth together without there being excruciating pain, what is it? what pain killers can i take?

Could be: If upper jaw could be sinus. If lower jaw could be tmj. Either requires treatment, not just masking of symptoms. Until you can get help take Ibuprofen exactly as directed on the package, but seek professional help asap. Call your dentist for an emergency appointment.

An abcess: Obviously you need to get to a dentist. It sounds like you have an access. Any pain killer that you buy without a prescription will help. Try something cold to see if that relieves the pain.

Likely within the TM: Sounds like a disc problem within the tmj. See an oral surgeon who is well versed in TMJ problems asap.

Severe pain: From what you describe i would guess that you have a badly infected or abscessed tooth. You can take whatever otc pain medication you normally take for a headache but i would not expect much relief in these types of situations. You need to see a dentist asap for definitive treatment, probably an antibiotic and an rx for a strong pain killer.