Technically, it isn't your 'period' if you are pregnant. A period is part of the normal monthly cycle and if you are pregnant, you wouldn't be having a normal monthly cycle. You can bleed, but if your bleeding is the same as your period, and you are having negative pregnancy test - you are more than likely not pregnant.
If your are concerned about possible miscarriage, please see your doctor.
And to the pp who said her friend had a really heavy period first...Uh...Ok? How in the heck would your body know it wasn't going to be the last period for 9months?