When using your laptop, basically set it in your lap or as close to it as possible. A good height on the sewing machne is crucial. I have a great sewing desk that is perfect height with my adjustable chair. Sometimes I sew at church with friends, or last week I took my machine on vacation with me and sewed at the kitchen table. It was not a good height for me. When it is too high for My shoulder gets to aching.
Frequent stretching. One thing I do (or used to when I could) is sit up straight, raise your shoulders up as high as you can then drop them as low as you can and try to leave them low. I have a habit, as my massage therapist put it, of wearing my shoulders as earings.
If you can't lift your arm up all the way you may have some impingement going on (bone spur) or you may have already frozen it up some. Get it looked at and get it moving or it will only get worse.