What Causes Menstruation While The Pregnancy Test Shows Positive Result?

I just found out i was pregnant yesterday via pregnancy test... but since that day i started bleeding and seems to be almost like a regular cycle.... my concern is that im miscarring? But I heard miscarring is very painful... i dont feel any pain stronger than minor cramps? could i be miscarring? and can i wear a tampon until the bleeding stops. And this is my second pregnancy.