Hi FTank,
Whiplash is a common cause of TMJ. It can go away on its own but 3 months is pushing it, so you might have to be more pro-active. Basically what has happened is that the ligaments, muscle, cartilage (all that medical stuff) gets stretched too much in a whiplash and can even cause the meniscus to get trapped out of joint (or just injures it enough so it has a harder time staying where it belongs).
Chiropractics can help but they do make me a little nervous because most (some) like to "crack." This cracking can cause arthritis further down the road. But I'm hearing that chiros has changed since I was last at one (15 yrs ago).
You should treat your jaw like it has been sprained (RICE - rest, ice, compression, elevation). Only problem is that we can't compress the jaw joint and complete rest is impossible. BUT, talking less, eating softer foods, no gum chewing, not opening the mouth wide, especially for any length of time (even to yawn or for a dentist) can be most beneficial. Use ice directly on the joint (using a towel) reduces any swelling and pain, and rotate with moist heat can get the blood flowing and also can reduce pain. Be careful to watch your posture especially your head and neck positions.
Once you think things have calmed down enough, there are exercises that can be done to strength your jaw (like PT). Physical Therapy can also be a big help (as long as it's done by a therapist trained in TMJ problems).
I hope and pray that you find the help you need. Whiplash TMJ can be "fixed," but it might take some time and "good" help. Take care.
God bless...
Carol