your diagnosis seems to be vulvodynia
your problem seems to be very unusual as its been recurring for quiet long duration and not responding to conventional therapies. a proper work out is required as this problem may be multifactorial like it may be allergic or irritant contact dermatitis
( eg from pads, vaginal secretions, latex
, etc.), any bacterial or fungal infection, neurological, some autoimmune disorder. i recommend you to consult a dermatologist first, it he recommend consult a neurologist as well. i also advise you not to scratch the area.