Hi all. Well, there have been some interesting developments since my last post regarding this persistent problem. Had the ultrasound done at a private clinic for a couple of hundred dollars - wasn't prepared to wait til August for the hospital appointment. Pelvic ultrasound was completely normal - no lymphocele, no abscess, no blood clots, no fluid build-ups, nothing! Everything in there looked perfect. So back to GP for further examination.
On consideration of the fact that the pain is present only when weight-bearing on right leg, and certain activities involving hamstring and adductor muscles, and the pain is absent when standing still, we've come to the conclusion that the pain is musculoskeletal - not neuropathic, as we thought. The thinking is that the surgery may not have caused any nerve injury at all - rather the pain caused by the fact that, following surgery, I had a month of very limited physical activity during recovery, and then started work and exercise again, stretching tendons and muscles too soon and too abruptly. Of course, the hamstring and adductor muscles are anchored at the ischium - right where the pain is centered. There might even be some irritation and inflammation of the ischial bursa into the bargain.
So - starting a programme of physio exercises for two or three months. Will continue painkillers as needed, but might replace the Gabapentin with Tramadol, as Gabapentin is only mildly effective with neuropathic pain and it now appears that my pain is nociceptive anyway, so Tramadol should prove far more effective.
Let's see how this goes!