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.