pregnantt?

My last period was July 22, 2007. It was only like 3-4 days and I usually have a 7 day period. My next period was supposed to arrive the 16th of August but still hasn't came. On the 11th of August I started spotting pink/brown and it was gone that night. The next day about 6pm I started bleeding redish-pink and it continued for 2 days. I don't think this was my period though. I was thinking MAYBE implantation bleeding? I did the Early Response hpt on the 16th and it was negative, but I am wondering if it were too early. I have been feeling tired WAY more than usual and my boobs are just starting to get sensitive. Not really bad though, just sometimes noticeable. Should the hpt test show positive tomorrow if I am pregnant??