Poor you, it is an awful thing to have! I read recently, that not only are Boots the cheapest for the tablets (all though I think it was sachets!) for this condition, but that they were also the most effective.
To you still have a period each month? It could be the ST's or, when washing yourself in that area, then you rub to hard when drying. -Best to 'pat' dry as round there is very sensitive anyhow.
But if it keeps coming back, then you are best talking to the Doctor about it again, could be a wee infection that's not cleared up with the antibiotics - maybe they weren't the right ones to take. Hope you get it sorted soon. X X