I suffered hamstring problems for years. One thing my physical therapist really did to help me was point out that my hamstrings were just the symptom. My hips, groin, Periformis, were all problems.

A good physical therapist will stretch you out and give you exercises to do to limber up and teach you how to stretch. Made all the difference in the world.

Also, if you can afford it, go see a masseuse. I bet the PT can recommend a good one. 3 or 4 visits with some deep tissue massages in combo with stretching will do the job.