Help!

My husband and I have been TTC for about 6 months. We didn't go off of birth control until right before we started trying. I was due to get my period this past Saturday, and didn't. I'm about 27 day cycles average, pretty consistent. I started light spotting on Sunday. Very light. Brown in color, and pretty much only when I wipe. Minimal cramping but not like usual period cramps. I did wipe one clot, but then went back to brown discharge. This continued for 2 days. Then nothing? I tested thinking it was implantation bleeding but it was negative. Could I still be pregnant and just not have enough of the hormone to show up yet? I usually always bleed for at least 4-5 days