Back/referring hamstring pain

Hi, I am a 30 year old female and have been active my whole life.  Around 3 years ago I was running marathons with no problems, no injuries and in good times. I got up off the couch one day and something went 'ping' at the bony area just above my right buttock. The pain went away but since that time (so for 3 years) as soon as I run, I get pain referring down my hamstring (it never goes to my calf area) and in my lower back (top of buttockreally, in that bony joint area).... i also get the pain normally, just day to day, its pretty much always there.
I have tried everything and seen everyone to get a diagnosis.
I have seen physios (x many), sports surgeons, back surgeons, sports doctors, had MRIs, xrays, ultrasounds, corticosteroid injections (with zero effect), been put on amitrip medication (again, little effect), undergone months of 'rehab' to try and strengthen my core, and my glutes, which differing specialists thought were weak. I have tried running/not running/doing nothing/doing something.  You name it, i've tried it (and for a decent period of time).
None of the tests came back with anything at all.
I am frustrated that no-one can seem to pinpoint what exactly I have - at least if I had a diagnosis I could adjust my life to fit whatever it is.  I would love to get back into running, and have tried for a wee while to just push through it, which just sparked it up more.
I really don't know where to take this problem next, I seem to have seen the best specialist in their fields, and to no avail.
Could anyone shed any light on this for me??
Many thanks!