Could I really get pregnant???

So I watch on my calendar when my periods are my cycles and ovulation times and I am on POINT with my cycle every month. My husband has been working really hard so we only had sex once this month 3 days before my period was supposed to start. I thought nothing of it since it was way past my ovulation time however I am now 3 days late on my period! I took a test just because and it was I think negative but how could there be a positive anyway after 6 days. Anyway could it really be possible??? I’m NEVER late except when pregnant and this would be number 8 😱