What Causes Pregnancy Test To Show Positive After Miscarriage?

I found out I was pregnant about two weeks ago,this past weekend I had went through every symptom of a miscarriage,cramping,bleeding,weakness,all the symptoms. Now 4 days later the heavy bleeding,blood clotting,cramping is all gone,but I am still testing positive for pregnancy. I have not had the chance to establish a Doctor as of yet,though I do have an appt. with an OB/GYN this coming Friday,should I wait or should I just make the trip to the ER?