In reply to Greg Cunningham:
I pulled my hamstring a few years ago, no idea how I did it as I don't remember a specific injury (it was just hurting one day, and more so the next day). I couldn't run for a good 6-7 months, and walking was painful for at least a month. Had some NHS physio and did loads of stretching to try and sort it after initial injury had subsided.
Didn't seem to massively impact my climbing, I went easy for a month or two.
No idea if you have just pulled hamstring, or something more, but I'd suggest at very least trip to the docs.
Post edited at 15:15