As far as temporarily relief, I like a cream/gel called BioFreeze. It was recommended to me by a physical therapist, and I have to say it has been much more helpful than BenGay or AsperCreme. You can purchase it on Amazon.com.
I also get trapezius pain when sitting for a long time at my desk. You may want to get up every 30-60 minutes and do 2-3 minutes of stretches to keep yourself mobile. Below are some youtube videos with exercises/stretches that may help:
I would suggest a complete physical by your doctor and a qualified Physical Therapist to review your posture, sitting arrangement at work and also find a qualified person to make sure your work area is conducive to your situation
I would then talk to your boss about taking a stretch/move break every 30 minutes for 2 minutes.
You may also consider hiring a Certified Qualified Personal trainer that can assist you with a workout program
Also: I realize you work long hours, however, consider getting up a bit earlier in your day and going for a walk for at least 20 minutes if possible, then another 20 in the evening!
Personally, I don’t recommend creams.
You may never have heard of MELT (Myofascial Energetic Length Technique). One of its components is a hand treatment which can have an impact on the hands but also moves up along myofascial lines and is often helpful with neck and shoulder problems. It can be done at your desk because you use small balls in a prescribed sequence. You can purchase this entire set (which includes a DVD, the balls and instructions) by going to www.meltmethod.com.
I am a trainer certified in MELT and have seen positive results when people use is regularly. I myself often use those balls for my hands when I have been at my computer for a long time. Note: it also has a sequence for the feet.
I wish you good luck
Many of us suffer from tight traps because we are always bunched up over the computer, Iphone etc. I have found for myself learning stretches for upper traps and strengthening exercises for the lower traps will help illiminate the pain. Relief does not happen over night but I manage the acute episodes and prevent escalation. I also use a tennis ball within a sock up against the wall to relieve pressure points or knots. I put my back on the ball and roll and massage the painful tissue.
As a student and a surfer I experience a lot of trap tightness and at night I apply Tiger Balm. It gives me immediate relief and loosens the muscles. You may want to check the ingredient label before applying. What works for me may not work for you.
Fibromylagia and arthritis are other stories, one I am sure you have discussed with your physician. Self care is about adequate rest, regular exercise, stress reduction, eating healthy, support, and doctor consult.