Why won't my 9 month old stop crying??

My 9 month old has been like this for a few weeks... He won't stop crying. He's literally crying all day unless he's napping. The only way he stops crying is if I carry him or sit down with him on my lap. I can't do that all day because I have other kids, I have to cook, etc etc

I didn't spoil him. He's never been like this, always quiet and he never really liked being carried. He'd go hours just rolling around by himself (and I'd let him), but now if I walk away or put him down he's FREAKING out.

Why??? My first cried all the time, newborn to 1.5 she just cried. But my son just started being like this out of nowhere!