Pregnancy advice needed!?

So I had my last period on dec.16.2010 last day. I had unprotected sex on the 22nd of dec. And a couple times after that. I had bron and light pink bleeding only when I whippd and not a lot on jan 3/6 and nothing since then.I took 4 hpt and all came out neg except 1 it looked like a very faint line but it could just be my eyes. Who knows. I have had some symptoms: very tired, earlyer on lower back pain and I was nausus but never thru up. Please don't judge I really have no one else to turn to and no adults I can trust to get me to a doc without my mom finding out I don't want to say anything to her until I know for sure that I'm pregnant if I am and I don't drive yet I'm 17. I don't understand why all the pregnancy tests would show up neg if I am preg. And if I'm not do you know any reason why I would not be getting my period? I'm not stressing about it no stress at all so that's not the problem. Any advice at all would be wonderful please be nice if not don't even bother to comment. Thank you guys.