How do i know if I'm pregnant..?

Well, I've been with m boyfriend for 6 months and as of 1 month ago we became sexually active. though as stupid as it may seem we have unprotected sex. One week we may have had an accident and to get checked out or take plan b. I was extremely broke because my job didn't give me my cheek until the week after (this week). I've been moody lately, i gained 5 pounds, I'm very nauseous and my period was supposed to come 4 days ago. my stomach hurts when I squeeze it in and it got me thinking what if somewhere within this month we had an unknowing accident?? but then again would i feel this way so early if i was only at lest a month?

I'm getting a test later today and i have an appointment monday but i would appreciate it if i get some opinions from everyone. Thanks.