Hamstring Trouble

Hoping I haven't encountered my first serious injury problem in my marathon preparation. My back has been a bit sore this week (bad posture at a computer I think), and when I went running yesterday I started to feel a twinge in my right hamstring. This afternoon I tried to do a speed session and the twinge came back even stronger and I had to stop. It's on ice now and I'm hoping a long easy run tomorrow afternoon will be easier on it. Otherwise I'll have to take some time off training which would be very disappointing.