I had mine done at about the same time. I don't have that problem, but have you tried physical therapy for it? It may be that there is scar tissue that hasn't released, or just that the muscle has to be brought back in some way.
I know you had psoas and bursa issues, have those cleared up for you? The hamstring I find is able to be stretched out if you take things slowly. It is a large muscle, so will take time to become limber. When I was teaching martial arts, I would tell the beginners that what they saw more experienced students do would take patience and time. A lot of that was based on stretching the hamstrings. Usually six months before they were reliably limber enough, and much of that was the hamstring.
PT and home stretching did it for me. Was your hamstring tight before the surgery?