I am going to take a guess and assume your upper traps are in a very lengthened state (especially the side with more issues) which in usually the case in people experiencing symptoms in this area. The upper trapezius gets in this lengthened state due to your body and in particular shoulders working to resist gravity. With all other body parts you body does a sufficient job to maintain upright erect position but the shoulders do not in turn causing the shoulders to be depressed. Most lose the kinesthetic sense of where their shoulders are and this causes the excessive tension or sometimes called repetitive strain.
I would work on getting the upper trapezius in a neutral physiological resting position (Not lengthened or not shortened). This will alleviate the tension built up in the muscle structure also allowing more fluid scapulohumeral rhythm.
For more information please check out my article about this exact topic.
Let me know if you have any questions.
Fuel the Movement,
About half a year ago, I started seeing a Rolfer. Rolfing is a technique for Structural Reintegration and mainly addresses connective tissue.
While my issue was nowhere near as severe as yours, it just dissipated at some time during the therapy sessions, and I have become a true advocate for Rolfing now.
Rolfers are few and far between but I hope there is one near you.
Have you asked your doctor whether it could be something neurological?
I am asking because this is certainly not the forum to find an answer to the source of your pain. This is way, way, out of all of our scope of practice.
Pain is indicative of a problem deeper than I can even venture a guess about. The only thing I can suggest is a second opinion.
I wish you well.
Oh! Have you tried rest?
On top of what Joanne posted..heat causes inflammation and is counter productive without an ice phase in the therapy..better yet just use ice, it not only brings blood to the area for healing (which is what heat does) but also reduces inflammation (which heat doesn’t do). Have you had a medical determination if its nerve related? could be an impinged nerve in the cervical spine, just that possibility takes it outside of a trainers scope of practice.