HCG/ Beta levels.....

So I got my results from the 4th blood test on took on 01/27/11.... They told me that the levels are good and that it was 4420. They still wanted me to get another blood test. The fifth one! I was curious why they wanted the fifth draw because they told me it's ok to schedule for an Ultra sound this week. Well I went in on Monday, 01/31/11 for a blood draw and got the results which was at 7172. Which they said that the levels were great! Ultra sound here we go.......