What Is The Difference Between Normal Periods And Miscarriage Bleeding ?

I have been have lower achy feelings in my adominal area. I am sexually active and trying to get pregnant so far i am having no luck. I have been nauseated soo much and thrown up quite a few times. I have have lower back pains, and all the pregnancy test have came out negative, i have also had frequent urination, and clear discharge, I just started heavy bleeding could I be pregnant or having a miscarriage?