I had big problems with neck/shoulder pain last season. I actually bought a larger bike because the fitter felt that I was too cramped up on the one I had. For me it was a combination of factors. I had (and still have,though it's better) a very foward posture just in general. My shoulders kind of slumped forward and I habitually had my head pushed out ahead of my body when I would walk or sit in front of the computer. So...I went to a chiropractor for a while and the adjustments helped, however, I ultimately ended up going to physical therapy to get rid of the inflammation and learn how to strengthen the area well. They showed me some alternate sleeping positions, too, which has helped. The PT has done wonders, though I have yet to test it on the bike outside on long distances.
My advice is get fit correctly, strengthen your core, strengthen your neck, shoulders, and upper back, work on your posture on and off the bike, make sure there aren't other things adding to your neck discomfort (having a poor set-up when working on a computer, bad posture when sitting, etc...), also if you have TMJ (clenching or grinding jaw/teeth), get that taken care of. That contributes to neck tightness/weakness/pain. The other thing I would suggest,too, is focusing on keeping your shoulders relaxed when you are on the bike. Several times I have found myself shrugging them upwards (tightening them) while I was riding. Try not to do that. On long rides, get off of your bike every 15-20 miles and stretch (with your helmet off). Make sure to increase intensity/distance slowly and give your body time to recover.
Heating pads/warm compresses can help warm those muscles up before riding and cold or warm packs can help after a ride. Massage is great, too, if you can spend the $.
I'd be happy to share strengthening exercises I learned with anyone who is interested. Feel free to PM me. Good luck!
