have they suggested therapy to help? How long ago was your surgery? Sounds like trismus (restricted jaw movement) which is common and takes being diligent with exercising the jaw to keep it opening and to get back what you have lost. There are gadgets available to help with this but my dentist said best way is to use thumb and forefinger to push them open, and then use tongue depressors to hold the jaw open several times a day.

i would speak to your doctors and ask for help in regaining the movement in the jaw and then really be proactive in the exercise plan. it won;t be comfortable, but it will be worth it. i wish you the very best through this difficult time.