Not crawling yet!

Hello,

My son is 8 months old (was born 5 weeks early so should really only be 7 months old) and isn’t crawling yet! Should I be concerned?? He sits really good and is very good a reaching and grabbing! Sometimes when he’s reaching for something while sitting he will fall onto his tummy! He never Really liked tummy time. He had bad acid reflux when he was born and tummy time made it worse. When he’s on his tummy now, he gets upset after awhile and rolls onto his back. He will push up on his arms. Thoughts anyone??