In my opinion, you do have TMJ (TMD, which includes a displaced jaw). I know that the pain is unbelievable, but you need to fight and find the help you need. Not all dentist are really all that familiar with TMJ and know how to treat it. That sounds like your father, I'm sorry to say. But, do not give up!! Stress is the number one enemy of TMJ, so you have to work at reducing your stress. Good REM sleep is essential for the body to heal itself.
Were you given anything (like Valium) to take at bedtime for just a couple of weeks? Has your bite splint been adjusted at all? Usually they need to be adjusted often when getting a new one. Smoking is bad mainly because your mouth has to work and you want to rest it to heal it. Once it's calmed down, certain exercises can be started. BUT FIRST:
Treat your jaw as if it is sprained. Rest it. Talk less. Use lot of moist heat directly on jaw joint. Use ice in a towel on jaw joint for 15 minutes throughout the day. Eat only soft foods and liquids. NO gum chewing or eating anything that requires chewing. Add Super Vitamin B Complex and Magnesium to your daily diet. The Magnesium, in particular, is known relieve grinders and clenchers.
Evaluate your posture. TMJ is becoming more common and I am reading where they (the experts?) think that our posture in front of a computer monitor is the reason why. The head should be over the reasonably straight back with shoulders back and down relaxed. The chin should NOT jut out towards the monitor but actually be down a little bit (not too far). Check out nismat.org/ptcor/tmj for pics and basic info. Also, make sure that your teeth are apart at ALL times. Rest the tongue on the roof of the mouth and keep the lips together relaxed or slightly apart. Sleep on your back with a good cervical pillow. If you can't sleep on your back, the side is okay IF you have a good pillow. DO NOT sleep on your stomach or put your arm under your head or chin. Breathing thru your nose, not mouth, is very beneficial.
Have your dentist or doctor refer you to physical therapy. Make sure that the PT is trained in treating TMJ. See a massage therapist, again, trained in helping TMJ. Intra-oral massage is particularly helpful but must be done only by someone trained in it.
Consider taking an anti-depressant. They are known to help TMJ pain (I know firsthand). It may take trying a few before the finding the right one. Other medications to consider are muscle relaxants, anti-anxiety drugs, anti-seizure meds, etc. There are several different kinds of meds within each classification and it usually takes trial and error to find the best one for you. (Example - over the years I have tried Skelaxin, Flexeril and Zanaflex - all muscle relaxers. Only the Zanaflex did any good.) Vicoprofen is the only narcotic I have found to do any good, but it can be addictive and should be closely monitored by a doc.
I hope I haven't forgotten anything. Self-help methods really do help but I must admit to be partial to regular therapeutic massage. Sometimes we find it necessary to adjust our lives in order to reduce stress. I can't emphasize how important this is. I had to change from a job I loved (but very stressful) to an almost boring job, but I love where I work. The change did make a huge improvement.
You can do this. Oh, I almost forgot that you must search for a dentist - neuromuscular or functional joint orthodics, etc. - who focus most of their practice is helping TMJ sufferers. Support sites, such as here, are valuable to TMJ sufferers because most people do not understand the pain of TMJ. Being in contact with other sufferers is good for us. Venting, getting ideas, etc. - all valuable.
Let us know how you are doing. Please take care.
God bless...
Carol