I'm so sorry to hear that you have a pinched nerve problem! I'm dealing with one right now,only mine is in my shoulder and has been affecting my back,shoulder,arm through the hand. Mine started the beginning of December, but I kept thinking it would get better by stretching,etc, but it didn't. I'd think it was getting better,then I was back to square one. I started going to a sports chiropractor that specializes in Active Release Technique several weeks age, and my shoulder is sooo much better! My arm was cycling between pain and numbness constantly and now I can even sleep on my left sde. The ART breaks down the scar tissue and adjustments help my neck and back. My pinched nerve,like yours,is a result of conditions that have existed a long time. My running is so much easier than it has been in years,as my arm swings freely now. I had no idea that I was about to have a major problem-the pinched nerve hit me hard! They are horrible! Get your treatments and ask your Dr. what you can do or not to help things. Mine has taken around four weeks of treatment,but I'm about finished. Luckily,I've been able to run,just nothing very fast to cause tension in my shoulder.Good luck!

I agree with Bob. Get your doctor to refer you to a good physical therapist. I have no idea where you live but an orthopedic specialist (OCS) or sports specialist given your running background. If one of those specialist is not available in your area any PT should be able to help.
Good luck. Being young should help.