Should i go to the ER for heavy bleeding & small clots during my menstrual cycle?

I had unprotected on 1/3/11 & took plan B on 1/5/11. My next expected start date for my cycle was 1/19/11 & since I had sharp pain in my stomach, I took a First Response early detection pregnancy test that showed I was pregnant on 1/18/11. Later the next day on 1/19, I had spotting in a pinkish color then later that night I had light bleeding. I called my OBGYN's nurse & she told me that its my period since I'm bleeding on my expected cycle date. I bled very lightly next couple of days until the 21st were it began heavy. Now being my 7th day of heavy bleeding & cramps, I wanted to know if this is my period or am I having a miscarriage. My cramps are awful but I can bare it but today they're off the chain mad pain. My OBGYN cant see me until the 31st. What should I do?