i started my period yesterday and usually I would have a heavy red flow of period blood. But when I went to the bathroom I noticed that it was brown blood usually like I would have at the end of my period. I know that brown blood means old blood but this is the first time that I can remember having it had the beginning. Today is day 2 and I still have the same color and flow of blood. Can someone please explain to me what is going on and if I should be concerned!

Also, I am very positive I am not pregnant because we do use protection and check after ALWAYS and I know the clear signs of being pregnant!

Thanks :)