Help?

So the last time I had sex was the first week of December and it was with a condom. I also went for a physical about 2 weeks ago in which they made me pee in a cup. Since I’m still under age my mom went with me and when they asked me if I had been sexually active I said no.

But since I haven’t gotten me period for some time (I’m irregular) I’m wondering if it’s normal to not get your period after having sex sort of constantly and then now not having sex.

By the way I took a pregnancy test a couple of days before going to the doctors but it was a small paper one and it came out negative.

Help? 😂🤷🏻‍♀️