Someone Please Help Me..

I'm extremely confused and desperate. My boyfriend and I had unprotected sex on the last day of my period. Well that was 11 days ago. Today, I found a lighter color blood discharge on my undergarment. I read about implantation bleeding and it scared me a bit. I have stomach cramps as well and have been really sleepy for the past few days. I don't know what to do. I'm only eighteen and really regret having unprotected sex that one time. I don't know when I can take a pregnancy test or if I should/have to wait it out. Is there any way to find out sooner? I would still have to wait til the beginning of December and I don't know if I can last that long.. Thank you if you care to respond..