LO not letting me put him down

My LO is 8 months old and still refuses to be put down. He cries and screams to the point of throwing up every time we try to have play time. It doesn't matter if I am sitting right next to him, he will still have a complete melt down. It seems like the only time he is OK with being down is when it's nap or bedtime in his crib.

I feel like he is falling behind in some of his physical milestones (can't crawl) because he is never on the floor, but I don't know what else to do. We have tried letting him cry hoping he will become distracted by all the toys, but every time it ends with him throwing up. Anyone have any suggestions? I never went through this with my first 2 babies, so this is new territory for me.