Hey S, the problem is most likely a neural irritation - and I would urge you to see an experienced physio to see exactly what interface is irritating the nerve. It may be a lumbar spine (lower back) issue, piriformis involvement, or scar tissue from your previous hamstring problem irritating the sciatic nerve, but an assessment would also rule out any other neurological conditions to be on the safe side. Its not likely there is any vascular problem (veins / arteries), as you would have pain, change in coloration of your foot, and it would be cold. Best of luck!