Upper Arm Issue

For about 2 weeks now, my upper arm has been hurting. The pain increases with the amount of stress on the arm specifically, not on the shoulder. I can do dislocates, and rotational stuff relatively pain free. Doing things where my arm is stressed however, like presses, pulls, back squats, etc, is a no-go. I can also flex my biceps and/or triceps hard for a few seconds without pain, but rather with a very slight ache afterwards.

The pain ‘feels’ like its in the bone, or right next to it, its deep pain, not in the biceps or the triceps muscles. But between the areas, really. Sometimes the pain radiates down to the elbow joint area, under the brachioradialis.

Any ideas what the issue could be?..a tendonitis or muscle pull/tear would cause me to have issues flexing hard, and bursitis with referred pain would cause pain while actually rotating, etc the shoulder, and it doesn’t. What could it be?