L.P.
Hmmm, has he ever had problems with reflux? The only times mine screamed like that were when they had reflux problems- one of the 4 had silent reflux.
Have you tried Advil or Tylenol in case it is teething? Maybe something about these particular teeth are causing him more pain? Or maybe several are trying to come out?
Sorry, wish I had more ideas. Hope he feels better soon!