Do not know if it pertains to your exact weight, but it could be weak muscles around your rotator cuff (Supraspinatus,infraspinatus,teres minor,subscapularis) if one of these muscles are weak they can lead to shoulder problems. I know that you said headache and neck problems are your symptoms. Just something to consider. With the shoulder being weak, your trapezius muscle (area above your shoulders) might be dealing with a lot more stress to balance out the weakness of your shoulder muscles. This might be leading to your problem. There are many different exercises that you can do for your shoulder to help strengthen that area. If your shoulder is not the problem, than maybe you should analyze the pain very closely and figure out what you feel is the exact reason for your sore muscles.
B.S. Exercise Science
ACE certified personal trainer
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Get the 5-7 out! Geez