hCG levels

I found out I was pregnant on Monday July 13th. My hCG level was a 7, just barely above normal. On Thursday the 16th my level was 49. It was doubling every 24 hours. This is my third and I started showing late with my 1st and second. My 1st at 7 months and my 2nd at 6 months. I was 10lbs lighter with my first 2. And at just 6 weeks and 1 day I feel like I am already showing. Has anyone else had a healthy pregnancy with such low hCG levels?