Is this my period or am I pregnant?

I'm on a birth control to where I only have my period every three months. A couple of weeks ago I was put on an antibiotic for a toothache and I have unprotected quite a bit of the time. I accidently missed one of the pills I was supposed to take this weekend, about three days before my period would be if I was not on bc (but I wouldn't have started anyway because it's not my third month yet). The day after I missed the pill, I started cramping and later that day I thought I had my period, but it was only a little amount of blood but it was not as dark as it usually is on my period. It was a light reddish color. It's been three days since then, and it's still barely there, and I'm still cramping. Is this breakthrough bleeding from the skipped pill, or is it implantation bleeding from having unprotected while on antibiotics? I'm mainly confused because I can't look for a 'missed period' because of the bc.