My baby boy was like that too. Would only cat nap and screamed all day. He had silent reflux like the other poster said her child had. Basically meant he didn't actually throw up but the acid was burning him going up him and then burning him going back down. He also wanted to be held a lot and he drank a LOT of milk. Apparently the excessive drinking of milk is because it sooths them to drink the milk....but then conversely resulted in more acid being created in the stomach to break the milk down..which then goes back up them...causes pain ,they scream, want more milk to sooth it and just is a vicious cycle.
So might be worth checking bub out for it. My boy had a pretty severe case and only grew out of it at about 8 months.