Yes, you should seek a TMJ specialist to help you with this. I worked as an endodontic assistant for more than 4 years. It is normal to have soreness/pain after an endodontic procedure for about a week or so. It is also normal to have soreness from the injections. I too have severe TMJ and when I had my root canal I had horrible pain radiating all over that side of my face. Root canals on upper molars take time, and you have to open wide and stay open for some time. This can cause problems with patients with tmj after the procedure. I would def. seek treatment from a tmj specialist. You need to call right away, because they tend to have long wait times to get in. You should call you dentist and ask him/her for a ref. to the tmj specialist in your area. Or a facial pain doctor. Your bite could possibly be a little off after having the procedure as well. Have your dentist check your bite to make sure the filling that the endodontist placed is not too high. They might want to adjust it down a little if it is. Again, these are just possibilites, as I have not seen your case.
If you had an infection in the bone around the tooth prior to your root canal procedure, the inflammation in the bone around the tooth can make the tooth push up slightly and feel higher than normal. This will go down when your infection clears up, but you may need to have your dentist make adjustments to the filling material to help with your bite.
I would call your dentist asap. I had to wait at least a month before I got in to see the facial pain doc in my area, and that was with the help of my boss (a dentist) getting me in quickly. Again, every case if different, and I have not seen your xrays or notes. There are many possibilites of what could be causing your pain. Do not wait for it to get worse. Go ahead and try to get in somewhere now.
Do you already have a custom splint for your tmj? The filling placed by the endodontist could have affected your bite, and the splint may need adjusting because of the changes. Wearing it with the new filling could actually cause you more pain.
I hope you feel better soon, but I waited too long to seek help with my tmj, and am now awaiting surgery to replace my joints on both sides. It started out right after a root canal and quickly progressed to the point that I can no longer work due to the pain. I am not saying that is what will happen in your case, but you can never be too careful. You don't want to end up where I am. You may be able to seek treatment from a tmj specialist, and get a custom splint and other treatments from them. They go thru extra training for this issue (TMJ) and have more knowledge than dentists as far as treatments for tmj disorders.
Good luck and please let us know how your treatments and diagnosis goes in the future. I will be praying for you, as I totally understand your concerns and pain.
You may want to find a TMJ specialis tsince severe tooth pain can be referred from muscles (called trigger points). If there is no other dental explanation that's a likely cause. TMJDoc