回复：最近左上臂疼痛，不抬高的时候不疼，但弯曲并抬高手臂的

If you did not have injury, it could be bicipital tendonitis or bursitis likely.
If you had injury, you need rule out rotator cuff tear by MRI.
If you rule out the both above, you may have suprascapular nerve entrapment.

YOU NEED TO SEE DOCTOR. IT IS VERY IMPORTANT FOR THE SHOULDER FUNCTION.