Period or implantation?

Savanna

I took a pregnancy test on Friday it was a clear negative!

I wasn’t suppose to start my period until today -the 28th. I started bleeding Saturday, super dark brown. Filled up two tampons and the rest of the day was light no clots or anything. Little to nothing Sunday. And now I have absolutely no spotting or bleeding. I’m not really sure if I should retest or what. 😐