What Are The Itchy Open Sores On The Labia Majora?

I'm 17, 145lb's and sexually active, we've had sex without a condom twice but he has been tested and I've gone with him and he's clean of any diseases. But for the past few days I've had two open sores on my labia majora and they burn and itch, but they aren't crater like. What can they be?