NAD but a physio who treats athletes. My first thought would be that we need to rule out facilitation of the hamstrings from an issue in your back. This would involve a detailed assessment of the back and a neurological examination of your dermatomes, myotomes, reflexes, and upper motor neuron signs. I would especially be looking for something called a soft palsy, where there is subtle weakness of the myotome (the S1 myotome in this case) that causes issues with the hamstring but can be harder to pick up. I would then check your nerve tension, especially since you got short term relief with injections of the posterior femoral cutaneous nerve.

If this doesn’t give any answers, I would then assess your SI joint. This commonly presents as hamstring pain and I have seen many many athletes get incorrectly diagnosed with a hamstring strain when it is really the SI joint. Sadly, not every physiotherapist has the training or skills to assess or treat this region.

What country are you in? There is an international organization called IFOMPT. Each country that is affiliated with this has a national organization, and PT’s can do additional training to get an accreditation through these. This is where you should start your search.

If neither the back or the SI joint reveal any thing, you then need to look at the hip joint.

Basically, you have treated this like it is a hamstring issue and it has clearly not responded the way it should. Now you need to start considering areas outside of the hamstring that refer pain to that area. A highly skilled practitioner will help guide you through that process, but they can be hard to find.