sitting pain

I have pain on sitting as though my ischial tuberosities bilaterally were made of concrete lumps plus it pulls/stings a bit down the verytop of my hamstrings. No pain standing or walking
MRI clear and bloods normal. Has worsened over a few years.
An UNGUIDED diagnostic injection into hamstring attachments by a musculoskeletal doctor in London eliminated pain whilst anaesethic lasted. As treatment I subsequently had dry needling and prolotherapy but this was ineffective.
Subsequent MRI of spine showed medium sized disc bulge touching nerve bilaterally. Back specialist speculated that the unguided injection had spilled over into sciatic nerve thus masking pain from bulge - however caudal epidural had no effect and subsequent nerve conduction studies indicated that the bulge not the cause of buttock pain.
No sciatica.
Piriformis is considered to be of normal length.
Have done a 12 week core stability machine based exercise programme and currentlly now do leg strengthening exercises -curls, leg extension and leg press. If anything I think this makes me worse in terms of stinging type pain but am persisting as its important to strengthen and stretch.
I wear orthotics uncomfortable flat feet.
SI joints do not give pain.
A few weeks ago had a GUIDED hamstring attachment injection. My hamstrings felt very relaxed but sitting on a lump feeling didnt go this time around!
Considered MRN but advised by a consultant radiologist that nerve imaging isnt up to much in UK - he has never read a positive scan even though on surgery patients have been subsequently shown to have some nerve entrapment. In the USA there are some specialist centres but that would be last resort as am in London. And I do not have any sciatica type pain. anyway.
So the really BIG question - where could the unguided injection have gone the first time around when it eliminated pain? I really didnt 'imagine' the pain had gone.
Myofascial pain perhaps (in gluteus maximus maybe?) - should I try trigger point therapy - I know that has to be followed up by appropriate exercises but could trigger point therapy at least be useful diagnostically?
Should I see a neurologist?
I would so like to get to a diagnosis - for example it could be that botox injections would help but its no good till we know where the pain is from.
Any thoughts would very much be appreciated.

You seem very well informed on the condition and nothing strikes me as obviously being the cause of your pain. I think trying trigger point therapy for diagnosis would be a good idea.
I'd like to know if you've had any more news however? Have you had a repeat MRI and is the disc bulge still pressing on the nerves?

thank you for taking the time to reply. I have now seen a pain management specialist who thinks the pressure pain has a hypersensitivity componet now and wants to see so has put me on Lyrica. But only 50mg for one week then 100mg for two weeks - my general practictioner seems to think such a low dose will have no effect but we will see and I will post if there is anything that will help anyone else.