My period is usually unregular not always on schedule. My last period was the second to last week in September. I had sex the 9th or 10th of October with protection of a condom and he didn't even finish. The day after I had sex I had a little blood but very dark and that only lasted 3 days right after. I was wondering if that could just be because of the sex or i don't know if that could have been my period. Otherwise if it wasn't I am late. Is this bad or what could this mean?