Hip injury

I’m a runner, and I’ve had a nagging “hip” injury for a few years now. On the outside of my left hip right at the waistline, where I believe a tendon attaches, I have pain that I think was cause by and is aggravated by running. It has varied in severity, but never completely goes away. Recently, the pain has peaked, and I decided to take time off from running to try to let it heal. I’ve taken a few weeks off before, but it never completely goes away. After, just a couple days of not running, I strained (perhaps tore) it while running bases at a softball game. It has been extremely sore since then (about a week). No pain when the muscles are relaxed, but hurts when walking, especially when going up stairs. From time to time, I’ve asked other runners about this, and I read a lot about running injuries, and I have never heard of anyone else having this type of injury from running or otherwise. I assume it is tendonitis; however, since I can’t find information about injury to this tendon, I don’t know how to treat it (exercises, stretching). I have not seen a sports doctor, but mentioned it to my GP once, who didn’t offer any suggestions.

If anyone has had a similar experience or has any suggestions, I would appreciate hearing from you.