It sounds like one of your discs may have slipped and is caught. Be careful at this point. Try "dropping" or opening your jaw with your lips together and lower jaw relaxed (teeth apart!) And for pain and swelling, if you are able, take ibuprofen/motrin (up to 600 mg with food) every 4 to 6 hours.
Even tho I don't have the greatest respect for doctors and many dentists when it comes to TMJ, you should go to your doctor or dentist. They might be able to prescribe Valium or Zanax or a muscle relaxant for the next few weeks.
This is the tricky part, at least in my experience. They might want to send you for a whole bunch of tests to eliminate anything and everything. My opinion is that if you feel it has something to do with your jaw, it probably is. Getting the muscles around the joint area to relax is essential. I would highly recommend getting a referral to a physical therapist who is trained in TMJ and getting there as soon as possible.
Right now - use your mouth as little as possible (no talking, soft or liquid diet). Do not pop your jaw even if it feels like you must. Use lots of moist heat around your neck. Try ice right on the jaw joint (in a cloth). ***Relax*** Go to nismat.org (physical therapy TMJ page) for important information on posture, exercises and basic information. Stress is your biggest enemy right now.
This is all for now. If the problem persists, find a TMJ specialist. Read the postings to Jodester for more self-help information. Do all the research you can. I have found that we, the patient, has to almost be smarter than the doctors when it comes to TMJ.
Please take care and let us know how you are doing.
God bless...
Carol