Acheing neck and heavy head

My neck has been aching 24/7 at varying intensities (worse on the left than the right) since January 2007 presumably as a result of intense bending over on many occasions throughout one week within that month whilst attending constantly to my computer. This problem is almost definitely coming from the trapezius and there is no discernable pattern to why it feels bad on some days and better on others. If you’ve ever been walking or running all day and had your legs ache at the end to the point where all you want to do is sit or lay down, then that’s exactly whats happening to my neck and that exactly what I do when it gets really bad as it feels sort of fatigued and my head feels heavy, neck sometimes feels tight too.
PARTIALLY SUCCESSFUL TREATMENTS CONSIST OF:
Heatpacks/ massaging- the problem was sometimes responsive to this and the intensity was temporarily lowered. Ice packs made no difference though.
Using 3 pillows instead of 2 - Seems to have had a permanent affect by slightly lowering the average and worst intensity of the problem.
1 muscle relaxant injection- this had a very quick affect on the headache (which is a common symptom for this kind of problem) and may have lowered the overall intensity for a short while or perhaps permanently.

FAILED TREATMENTS CONSIST OF:
Standard pain killers: - such as Ibuprofen, another slightly more powerful one and dosulepin.
Posture improvement- My posture is actually a lot better than it’s ever been (I stand and sit much better) but annoyingly this hasn’t affected my problem.
Physio therapy excercises- Loads of different exercises were done over the course of several months and they either made no difference at all or temporarily made the problem worse.
Mri scan- Showed up nothing of concern at all
Acupuncture- Done once per week for 5 weeks, but made no difference.

The pain management doctor sort of though it could be muscle spasm, but what else can I try to help me or at the very least what other problems can one have from their trapezius that share my symptoms?