Small baby?

Justia
My baby is 8 1/2 months and she weighs 15lbs 12oz. She's 28.5 inches. I feel like she hasn't gained much weight since 6 month appt and she looks very slim and slender. Based on the norms she is on the low average end. Anyone else has smaller baby? 
Also she's not crawling , doesn't roll over completely, no teeth yet... I'm beginning to worry 😓