I got a similar injury in nearly identical fashion a couple of years ago. First track workout of the year, some time in February. A twinge in the area where the hamstring attaches to the glute, didn't really feel anything until after I finished and was limping home. Even then I didn't take it seriously enough and ran on it a couple of times before deciding that was a bad idea. I think it was a gluteal strain in my case, and it took a very long time to heal. Rolling it with a lacrosse ball was excruciatingly painful, but I think it helped.