Vaginal irritation. Help!

Okay so I had a yeast infection, took a 6 day Monistat thing and it went away for a day and then the next morning I had vaginal itching and small amount of discharge again. I have no STDs, I'm not pregnant, I don't use any strong soaps or vaginal deodorants, I wear nothing but cotton panties, I'm on birth control but I recently missed a period. What could it be? Is it hormone imbalance? What should I do?