Help me?

Soooooo I might have ended up having unprotected sex last month and now I'm getting really worried I might be preggers... I was supposed to start my period on the 6th and I have irregular periods, but there was some colored discharge on my undies from overnight on the 6th but nothing near a period I've ever had. After that, no blood. I've been very tired, sleeping 10-12 hours a day, I've been light headed and dizzy, almost threw up once from it, and I've been emotional alot too but that might just be from being tired, hot (from wether), and stressing about possibly being preggers. I'm 4 days late today. Do you think i could be pregnant? When should I take a pregnancy test? And what brand do you suggest? Is dollar store brand Okay? Thank you in advanced!