8 days late? Implantation bleeding???

Can someone please help me out here! I had sex for the first time 2 weeks ago and it was protected with a condom. I still haven't gotten my period and I am 8 days late. 
I took a test but it was negative but I'm worried I didn't wait long enough for the test to show results. I took in the morning in a rush.
Two days later, I got a brown discharge spotting. I read up on implantation bleeding. 
I'm gonna take a test again but am I just being paranoid? I really can't be pregnant.

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