Pain in Left thigh muscle

I have been jogging every other day for four weeks. Taking it easy jog/walk routine.

I have developed a pain in left leg thigh muscle. I warm up and stretch before and after jogging. Am in good health and do not drink or smoke.

Any advice on this problem and how to stretch properly.  

Hi Jules, newbie here so take this with a pinch of salt please. Many people suggest you don't stretch cold muscles and either don't stretch before a run or do it (say) 1 mile into your run). I take it you have properly fitted running shoes?  Is your route on a camber? if so you me be putting your gait out of line. 

Hopefully somebody will be around soon to help you out with your pain.

Thanks for the advice. Cheers