If you got your period a week early and it is still going but has been bright red and has a lot of dark red clumps and you have had cramping and vomiting could you be experiencing a miscarriage?

Possibly, but it could just be a heavy period. The clumps and cramps worry me though. You should call your doctor and talk to them. There are things that need to be done a lot of the time after a pregnancy.

go to a doctor right away.