Tendonitis in my Left Arm

I have recently come to the conclusion that I have tendonitis in my left arm. I get pain when doing certain movements. This is where the pain is located: 45 degrees to the left of the vein. I have a hard time doing overhead presses, dumbbell curls that are angled towards the outside, and sometimes I have a hard time flexing my bicep or making a muscle. I would like to know some suggestions for how you have dealt with tendonitis.