HCG Levels

I went to the doctor last Thursday and found out I am pregnant. Totally unexpected and a complete shock. I have had irregular periods for the last 3 months but have had one until this month. I have had nausea on and off for a couple months and have had some swelling in my legs. I thought it was a thyroid problem and had no clue I was pregnant. Today the doctor called me back and told me my HCG levels were extremely high and they want me in right away. I looked it up online and it says hay can be caused from being farther along than normal, an abnormal pregnancy or being pregnant with multiples. I feel little flutters and have for over a month that I thought was just gas. My mother, first cousins and aunts are twins. Does anyone have any advice, suggestions, etc? I am terrified that something is wrong