Every 15 Minutes

Simon's seriously crying and screaming pretty much all day. It's the screaming that is most disturbing. He's almost 4 months old. I don't know what to do. Everything seems to be getting worse. There's no obvious reason for him to be so miserable. He can be calm for maybe 15 minutes at a time, and then he's back to crying. I really can't stand it anymore. I guess we're both miserable.