I am a Licensed Massage Therapist, and I have some ideas for you. First of all, since you are sleeping are your side, try training yourself to sleep on your back with a pillow under your knees. It may be hard at first, but it will keep your spine in better alignment. If you have to sleep on your side, then buy a body pillow, and make sure the pillow for your head is offering adequate support without causing your neck to be tilted up too high. Also, I would encourage you to see a chiropractor. More than likely, you have an issue with one of your cervical vertebrae. If you see a general physician, they will give you medication, which won't solve the problem. Also, it is possible you are dealing with carpal tunnel. If you use a computer throughout the day, make sure you have one of those gel packs to support your wrists when you type on your keyboard, and when you use your mouse. Lastly, feel the muscle under each arm. If it feels large and bulky, then try consistently using ice under the armpit. If this muscle, ( the supscapularis) gets too bound up, it can cause pain, and numbness and tingling. Also, consider going to see a massage therapist. I know it's expensive, but a good therapist will be able to determine whether or not the issue is muscular. Most importantly, go see a chiropractor!!!! MANY chiropractors are fairly affordable and even offer massage as part of their therapy. My concern is that this problem will become something you deal with during the day if left untreated.
Blessings!