HCG Levels not doubling and super worried!

Monica
So I went in to the ER Saturday because of some spotting and my HCG levels were 6,333. I'm about 5 1/2 weeks pregnant. I went in Monday to get them checked again and I was at 7,400. My dr said they are increasing but not at a rate she would like, so I have to go in Friday for an u/s and some more blood work. Has this happened to anyone else? This is my first baby and the spotting stopped. I am feeling nauseous, but otherwise pretty good. I'm so worried!! I'm not sure what the HCG levels are suppose to be? Can some of you post your levels if you know them?