First of all is it possible for you to attach a photo of your X-ray here?
Is any tooth carious? Do you have bleeding gums? Did you happen to bite onto anything hard from that side? Did your dentist rule out wisdom tooth related issues? Are you regular with your follow ups for multiplesclerosis? Do you feel any sclerosed areas on left side of face intra-, extra-orally?
Many questions are unanswered in your query.
Do you feel your problem is more severe in the morning after getting up? If so that could be simply MPDS also. For that you would need muscle relaxants. But before following any prescription from an open platform my sincere advice to you would be to consult a good, well qualified dentist (preferably an endodontist or oral medicine specialist), close to you and discuss the prescribed dental medicines with your treating physician before starting it.
Next Steps
Keep practicing mouth opening excercises, Also discuss your dental problem with your treating physician.
Health Tips
Don't follow instructions from an open platform as your case may require a multidisciplinary approach. Good luck :)