Lack of proper natural lubrication.

The before sex foreplay can get me wet. Being fingered and ate out can make me wet. But as far as the way he kisses me or bites my neck *i love that shit** most of the time I can't get wet. Ans sometimes even after I'm wet, of he pulls out to change position or we go from foreplay to actually having sex, I dry up. It's like instant almost. I don't understand what's wrong with me. I haven't always been this way. Just in the past 3-4 years. Help. Please. It's embarrassing and has caused issues in past relationships. I don't want it to become one in this one.