Ultrasound done and reviewed - I have calcified hamstrings where they attach to the sitbones: likely causes: pressure, wear and tear, over-stretching, and muscle imbalances.
Previous steroid injection didn't help. I'm now being referred to the hip consultant at the local hospital for possibly another injection under ultrasound or x-ray.
I've also found a sports therapist who is really positive and optimistic for my recovery; the first professional to actually try and understand why the injury occurred; hypothesising that my back and hamstrings were over compensating for a weakness in certain parts of my glutes. He's given me strengthening exercises which i'm working away on.
No cycling or running at the moment, just swimming, walking and pilates.
Still hoping to get back to cycling - maybe next year?!