HCG Levels

I am only 4+2 but have had my HCG checked a few times due to previous losses.

1st Draw - 38

2nd Draw - 149 (48 hours)

3rd Draw - 292 (46.5 hours)

Should I be worried that even though levels doubled from the 2nd to 3rd draw, they were less of an increase than the prior draw? My second draw almost tripled but I barely squeaked by with a doubling on the 3rd. Hope that makes sense!