Baby crying all day
There are quite a few reasons why babies cry. I had a very short list with Charlie when he came home from the hospital. Change his diaper, feed him, burp him. As he's grown some that list has grown to add: is he tired? Is he bored? Is he sick of sitting in one place? Does he want to get up and walk around? Or does he just need some snuggles? (or has mom just sat down to a hot meal? does mom have to use the restroom? haha)
If you've tried your own list of questions that you've gathered and nothing is working, it might be time to see your pediatrician. He can be constipated and it's hurting him, he may have some gas that's stuck somewhere, he can have reflux! All things that we cannot see with our eyes. A pediatrician can identify those problems and help.