What Causes Pain While Stretching The Arm?

What does tendonitis in the upper arm feel like? I have had an ultra-sound to rule out a blood clot and took scheduled anti-inflammatory medication ( Aleve ) for two weeks. Symptoms are better, but not back to normal. This is not in the shoulder but in the muscle part of my upper right arm. Certain moves cause pain and cannot lay on my right side at night. Stretching is painful as well as crossing my arm over to my right side either in front or behind my back.