hcg not doubling

Leah • Mommy to a beautiful rainbow baby; Adaleigh Rose 🌹 💓
I went in 11/08 and my hcg was 13,811 two days later on 11/10 my hcg levels only went up to 16,278.
According to LMP I am 7 weeks 6 days, still haven't seen a baby on the ultrasound. 
Are hcg levels always supposed to double? Or does this mean I'm close to miscarriage?