Was the sex rougher than normal? I once had very rough sex and one labia swelled up and I could feel it pulsing. It lasted a couple days. I would try applying Vaseline to ease the irritation. If it lasts more than a couple days go get checked.
I wouldn't self-medicate with Monistat just yet. I'd suggest wearing cotton undies and washing with mild soap to eliminate possible sources of irritation. Call a doc if it doesn't go away in a few days.