Sex with boyfriend?

We're both 17 and have been dating for almost 4 months now and we make out, touch each other through our clothes, etc nothing major and we set goals for when to do certain things but I was wondering when could we have sex? I'm actually not a virgin which is hard to explain as to why without people calling me a slut and I'm my boyfriends first girlfriend. My mom told me that when me and my boyfriend are thinking about it to tell her so I can get on birth control but I want others opinions on when to have sex?