Hcg levels

Hello!! I was hoping for some advise. I had my hcg level done 11dpo and they were 17.8. The doctor had me go back in 72 hours because it was low and at 14dpo they went up to 111.4. My sister has to go to a fertility specialist and they said numbers should only double in 48-72 hours and mine went up 6 times. Anyone ever have this happen. Doctor said everything seems good and I have my first appt on dec. 3rd. 
This is my second child and I've had one mc in September.