Help with being "wet"!

This is a little embarrassing but me and my boyfriend have never had sex and im a virgin. When we make out and stuff i get wet down there. My mom asked me today if i was on my period and i said no. She said there was stuff on my underwear and i told her it was sweat. I dont know if she really knows what it is or not. She said it was worrying her. I dont want to tell her what we been doing! How do i hide it!