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,