Why did my period start 11 days early?

My husband recently got a vasectomy reversal at the end of December. Since then, we have had in Januaruy (expect for the days I was on my period). At this point, we are not sure if the procedure was sucessful due to him having his follow up appt later in February. Well this week, I got my period. I started to spot, then eventually started my period exactly 11 days early. My period is normal, & I am healthy. However this period was different. Its brighter in color, and just different. Can anyone shed any light? Is there a possibility I can be pregnant? Can someone take a pregnancy test while being on their period?