Throwaway here, looking for a not-awkward way to tell my mom I've been having sex. Any suggestions?

I'm in my early 20's and have been having sex for a few years, pretty infrequently. About a year and a half ago I asked my mom if I should get birth control (as I'm still on my parents' insurance, WOOHOO!). I asked her under the guise of getting it for my period because we were in a public place, and frankly I was chicken. So she said that I probably shouldn't use it strictly for that purpose since it could mess with my hormones and shit, and if I was having sex I should get them, but if not I should hold off. This made sense and I agreed, since I wasn't seeing anyone or planning on it.

A few months ago I went to a doctor for an unrelated visit, and she asked if I was on birth control. She wrote a prescription for ortho tri cyclen, which I still have not filled. I haven't filled it because I spoke to my mom again about it and she asked if I was having sex, which again I was not (at the time).

Now, I'm sort of going out with this guy and still not on birth control. We haven't had sex but I see it happening in the near future so I feel like I'll have to admit it to my mom sooner rather than later so I can get me some birth control. Any advice on how to make it less awkward?