Two periods?

So the last time I had unprotected sex was Jan 9th. Took a test before my period came, negative.

I got my period on the second to last week of Jan 22-26.

But now my period started again not even a week after it ended ? Feb 1st. And it’s heavy. What could this be? I also have been on the keto diet for a month now. I’m going to take a test again today.