this is exactly why i quit doing passive stretches.....it can be easy to over do it and fuck something up. this same thing happened to me last year, it took a few months to get better...
i didnt mess with it for a while and it did get better bit slowly. basically you overstretched it. (nonscientific explanation i know). now all of my "flexibility work" occurs "actively"- i dont force any stretches at all... i move myself into the stretch as part of basic range of motion drills (pushups, squats, pullups, side bends, stuff like that. Dont force stretches, they can fuck you up bad. Another reason I dont do yoga..seriously, i know more people who have fucked themselves up from yoga by forcing stretches and such....
V