Hi, I was wondering that isn't possible for a women to be pregnant and be on their period at the same time ?? what are the chances?

Also, how would I know if there a different between period or implantation? I heard that some women could mistaken that the bleeding vs period and also bleeding could be a sign of early pregnancy, is that true? I did some research and it say early bleeding that could be a sign of early pregnancy could last between 2-3 days, isn't possible for it to bleed to last longer? plz help!

thx you for your time!