I had abstinence only education and don't understand pregnancy?

If I had sex on December 28th, one day AFTER the end of my period, which period would be missed if I am pregnant? The immediate period, or the period I am supposed to get in a week? I had a normal period a few weeks after having sex, so does that mean I'm not pregnant? 
And of course, I grew up in a rural area where we never learned this kind of stuff, so please don't come at me with the "I shouldn't be having sex if I have to ask". I am an adult and I use protection, I just never learned some pregnancy stuff. 

Glow Resources

Let’s Glow

Glow is here for you on your path to pregnancy

Glow helps you navigate your fertility journey with smart tools, personalized insights, and guidance from medical experts who understand what matters most.

25+ million

Users

4.8 stars

200k+ app ratings

20+

Medical advisors