Hi there angie,
I'm sorry to hear that your period hasn't come yet! That can definitely be stressful.
However, if you took a pregnancy test correctly after the day that you expected to get your period, and it came out negative, you can be sure that you're not pregnant.
I think Heather already shared this article with you before, but just in case you need a reminder, there are a whole lot of reasons that periods can come late:MIA, or Dude, Where's My Period?
In all likelihood your period will come soon, and right now it's just a waiting-and-taking-care-of-yourself game.
In terms of this last sexual encounter - what forms of contraception were you using (if any)?