15 dpo and started spotting? So confused!

So my husband and I have been TTC for a few months now, and AF was due yesterday. I woke up yesterday morning and when I wiped there was a tiny bit of brown blood, so I assumed AF was starting. As the day went on I still only had very light spotting and it was not pink, it was brown and barely enough for a panty liner. I had taken a hpt at 12 dpo and it was negative so I figured we were out this month. I woke up this morning and it's the same spotting still, barely noticeable but still no period like blood? I'm so confused now and am waiting for my hubby to wake up to go buy another hpt since I don't have any left (ok, I am a little impatient) but I had taken a few tests early since last night was my hubbys 30th bday party and I was really really hoping to surprise him with being pregnant but when I woke up with spotting I figured that wasn't going to happen this month. I know it's late for implantation bleeding so I'm all sorts of confused and going crazy, as if you couldn't tell! HELP! Am I just going crazy??? Lol