As a 26 year old mountian biker/snowboarder/road cyclist/motorcyclist, I highly recomend the bone cracker!!! They will diagnose the problem and suggest stretches and excorcises to help strengthen the areas needed to support the shoulder. My right side neck and shoulder sorta near the shoulder blade gets sore on long rides, or even long car drives due to a few tweaks I did 5 years ago as a ski bum, on the mountain, I didn't take care of it then cuz I was 22 broke as a joke and figured a bit of time will heal it..... Well 1000 in Chiro and massage in the lasst two years is really making some progress, that could have been fixed in a couple of months back in 2000!!
In the short term look up some stretches for your pecks, often the cause of shoulder and neck pain on a bike, is that your not only reaching forward with your arms but your shoulders as well, when in fact you should try to maintain shoulders back and straight. This will cause the pecks to tighten up over time, and distend the weaker muscles in your back and tire them out. one stretch I find super usefull is extend your arm straight out to the side, with arm bent at 90 degrees up (like turning left motorcycle hand signal,) put the forarm on the edge of a door way, and then step forward, leaning against the arm, you should feel a good stretch in the shoulder pectoral area, try varing this stretch with arm up at 45 degree... I do this regularly on long rides, and has helped imensly in my shoulder recovery. Sorry if this is a little long winded, but its something I've had to really deal with, because I love long rides, and it really sucks being a "young fit guy" who has trouble riding a motorcycle due to shoulder and neck pain!!!
I'm not a Doctor nor pretend to be an expert, just thought your issues sounded very similar.
G
Grant.