So, I've been on antibiotics last week and only just realised that the pill doesn't work on them. So I've had unprotected sex on my predicted ovulation. A couple of days ago I had some blood but it wasn't normal, it was quite light and almost like discharge mixed in with it. I stopped my pill early as I was worried, I would usually bleed at this point. I took a test two days ago but it was negative. Could I be pregnant?