HCG levels

Nakita • Baby 1- June 2015, Baby 2- October 2016, Baby 3- March 2018!
So just got my first blood results back.  They can back at 576 and were taken last week. Doctor said I wa about 3 weeks along (since ovulation) and he said I'm doin fine but he didn't take anymore blood to see if my levels are doubling ?! Should he have done this? Should I be worried?