What to do about back pain!

My lower back has been killing me. Mostly the right half, right next to my tail bone. I have not done anything out of the ordinary to strain it or hurt it. It has been sore over 4 days now, and i have been consistently stretching it and taking Advil. I sat out of track practice today because of the pain. Its mostly spasms, when I’m sitting or standing up, a shooting pain goes right through my lower back. Any further suggestions on how to cure my back!?