I think i have a swollen jaw muscle that has cause some sort of swelling towards the back corner of my mouth towards the molars. i am scared it may be?

TMJ: You may have muscle spasm from clenching or grinding your teeth. See a dentist that specializes in tmj, they can fit you for a mouth guard to wear at night and prevent progresison of the problem.

See below: May be decayed tooth, dental abscess, or a partially erupted 'wisdom tooth'. Mumps is unlikely if u had all your childhood immunizations. See your dentist for exam & probable radiograph (x-ray). Nsaid or tylenol (acetaminophen) may provide temporary relief of pain and swelling as may ice applied to area. But see dentist soon.

See a dentist: If you have facial swelling of the cheek that you notice when looking in the mirror, it would be very important to see a dentist to evaluate for an infection/abscess. There may or may not be pain associated with the tooth, but likely will also be associated with tooth pain in the mouth. Alternatively, it may be a tight muscle from bruxism but that is less likely from your description. See a dr.