HCG levels doubling every 84 hours?

Samantha

I’ve had my hcg levels monitored:

4w1d 124

5w5d 6660

6w2d. 14790

My numbers seem low to everyone else on here. My levels doubled within 48 hours between 4-5 weeks, but took 84 hours to double at 6 weeks. Should I be worried? My ultrasound isn’t until Tuesday.