I have torn my UCL, once and than again. My pain was located where the UCL is, with some upper forearm pain. Could not bend my arm straight for a long period of time. I believe Matt Harvey had forearm discomfort.
If the doctor said you have no structural damage and your arm appears to be healthy I don't see how it could be your UCL unless it just recently happened. Did you get a MRI?
Definitely schedule another appointment with your doctor if the pain continues.