I have 43 days menstrual cycle, my LMP was on 5th July 2012, I tested for blood hcg on 20th aug 2012, it was 4057.9, then after 10 days ( on 30th aug 2012) again I tested for blood hcg and it was 17436.4. I am worried because I guess little low as compare to normal levels. What should I do?