I had 3 ACL recons., last one was 6 mon ago. 2 & 3 used patellar allografts. I still get hamstring pain doing concentric exercises. What causes it?

Incomplete rehab. Hamstring allografts often cause pain in the post-op period but rarely cause prolonged pain or functional problems. It may be sciatica (nerve pain) but if it is coming from you hamstring a pt that can help with an eccentric strengthening program and manual treatment to break up adhesions usually helps.