I Was Diagnosed With Tendonitis Of The Lower Arm About

I was diagnosed with tendonitis of the lower arm about 2 weeks ago and have been on Naproxen for inflammation, but the pain isn't getting better. Now my upper arm (outside of the arm) is sore to the touch and there is a slight bulge in the muscle directly below the elbow like a really tight muscle. I wasn't sure if I should limit use of this arm (it's the left arm). It really hurts a lot when I am driving. Can you give me some advise?