This sort of after effect is quite common i think,depending on which muscles and nerves you had removed or were damaged during your surgery.Rob had his sterno mastoid muscle removed but they managed to preserve his shoulder muscle,but even so at 5 weeks post tx he started with terrible neck stiffness and shoulder pain,and it got much worse if he got a draught or was out in the wind or the cold.Our GP said it was unlikely the cancer pain meds would help and suggested anti imflammatories and soluble paracetamol.I also rubbed his neck and shoulders with topical anti-imflammatory cream.I was always telling him not to hold his neck stiff as this increased muscle spasm.So best suggestion i can come up with is heat,exersise and pain meds.I have heard that exit site for radiotherapy in the shoulder can cause bad neck and shoulder pain.