Welcome to the MedHelp forum!
Your problem looks more like Pudendal nerve entrapment (PNE). PNE results in chronic pain, in which the pudendal nerve (located in the pelvis) is entrapped or compressed. Pain (felt as pricking, stabbing, burning, numbness) is worse on sitting. The diagnosis is made by a neurologist by clinical examination, MRI or CT scan, Pudendal Nerve Motor Latency Test (PNMLT) and by giving a diagnostic block. Since you have exhausted all other possibilities, you can take a look at this.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!