Higher HCG levels- signs of twins or just a really healthy baby?!

We found out we were pregnant 5 days before my missed period with an at home test (which shows results of 6 HCG or higher). The next day I went in to get blood drawn, level was 51 (4 days before missed period) two days later it was 150. One week later it was 2901. 5 days later, so today, it was 13,558. I am five weeks 2 days pregnant. That number just seems crazy high to me! Anyone else with similar results?!