Crawling

So my baby girl is 8 months old now and she’s still not crawling. I feel like maybe it’s because she’s a bigger girl. April 1st she weighed 20lbs, so you can get the idea of how big my chunky babe is!

She’s good at getting to her hands and knees and she kind of rocks back and forth but still nothing. I try my best to always put her on her hands and knees but she just gets frustrated when she doesn’t go anywhere so she lays down and just rolls everywhere! Please give me some tips on how to help her!