How To Know If I'm Pregnant, My Last Period Was March 13-17, I Need Help?

It is probably too soon to tell, i would wait another week or so. However, buy a couple pregnancy tests from the store ( the ones from dollar stores work just as good as expensive ones.) It is your choice which one to get, take one first thing in the morning, with your first pee as you  have more hormones then so if you are it is more likely to show up. If it says no wait a couple days and take the other one, You can still be pregnant even if you get your period. If you get a positive result or still think you are after tests see a doctor.