I've had no hamstring problems for years until just recently on my last two easy runs about 2 miles into the run my hamstring will give me a sharp twinge and then proceed to get worse like a full-on pull forcing me to walk. I'll walk for a while then stretch and I'm able to complete my run but can't really push it at all. The next day it will be a little sore and tight. This has happened on two consecutive runs first my left hamstring then my right and has me totally confused as what the cause might be. Things that have changed since the race season are Ive gained 10 lbs, started light weight training with legs (only 60 lbs on squat and bodyweight lunges). Coffee consumption has not changed but I did switch drinks with a little more caffeine (ive heard coffee can cause cramping but I've always drank coffee).

Whatever it is I'm baffled as to what could be causing it. Any thoughts?