Hi ! Generally hcg levels in pregnancy tends to increase by 2 times in a span of every 3-4 days or almost every week, till 1st trimester i.e 12 weeks, after which it remains stable to tends to decrease, how ever hcg levels differ from one to another during pregnancy. So u need not be worried if it is not exactly doubling, but definitely u will observe considerable increase week by week as the pregnancy advances. As per ur given data ur hcg level by next week would be aorund 6000- 7000. But donot worry if it is the border level. For the present ur hcg report is nrml.