pimple type cyst in between legs near bum and girly parts.

I have this cyst/pimple on bum cheek where is kinda meets my girly pits. I have "popped" and drained it twice now it really hurts to walk and I am just wondering when should I see my doctor? When it comes up its between the size of a 5c/ 10c coin (AUS) I really just need so pointers.