Could I be pregnantt!? Please help! Neg. pregnancy test. ?

I need help on whether I could still be pregnant or not. I had unprotected January 15th, 16th and 17th and he probably came in at least three times. My last period was December 30th. I am due for my period by the end of this month and I took a First Response test and it came out negative. Is it possible that I am still pregnant? I've been feeling a bit off, very tired, moody etc. I know implantation occurs about week after fertilization and that would've been this past weekend. And that hCG isn't present right away. I've also been experiencing excess l discharge. I don't know! Help!