Why do I suddenly become dry

Hi so recently I've (20F) run into this situation where the last couple times my partner and I tried to get on the freak train everything started great I was well aroused and wet and then by the time they get protection I'm no longer aroused. Dry. And no matter what it just kinda stays that way and I can't turn back on. I really don't get it. Any ideas why or what it could be?