First of all do not panic. All you have to do now is to see a good obstetrician immediately. Implantation
bleeding is common in many cases and many-a-time, it looks like an ordinary period. Also, it is not quite common for a pregnancy
with a regular gestation sac to abort. Yet, since you are experiencing pain, you may need a sonogram to know the outcome of your pregnancy and treatment depends on that.Wish you luck.