Immunity to monistat?

Well, your body can't really develop an immunity to monistat. It's the yeast you're worried about. Here's the thing - if you don't keep blasting it with monistat (and soon) it might continue to mutate and get completely out of control. (This is the same reason why they tell you not to stop taking your antibiotics before your prescription is up, even if you feel better, because if it's not totally gone, then it can mutate and get unmanageable.) Your best bet is to get rid of it as quickly as possible. Take the monistat.