I had oral sex yesterday and woke up this am with jaw pain. Could this be my tmj?

Yes! Interesting story and situation. If you strained your jaw wide open, you could have sprained your jaw joint, or tmj. Under these circumstances, it probably won't' last long. You should try a soft diet and "baby" your jaw for a few days and see if it doesn't go away. You might, if there are no contraindications, benefit from a non-steroidal anti-inflammatory medicine like ibuprofen, or even tylenol (acetaminophen).
TMJ Strain. Tmj pain characterized by pain and tenderness in front of the ear canal. The pain is often aggrevated by jaw activity and relieved with rest. Sprains or strains of the TMJ from any number of causes do occur. You have likely strained your tmj.
Just fatigue. In most cases facial and jaw pain is related to muscular fatigue. Chances are that you are grinding your teeth at night as well. Consult with your dentist.
Yes. Common to have TMJ symptoms when mouth is open too wide. Should settle down. Don't aggravate it again until symptoms dissipate.
Acute or chronic. If this issue has been happening quite often, even for other functions of the jaw, i would see a dentist and/or tmj/tmd specialist.