I went thru the same thing 2 years ago. He needs to see the nutritionist assigned to his radiation oncologist. A gradual feed (80ml per hour of formula with 150 ml of water every 2 hours) using a pump at night finally settled things down for me. Suggest formula of either Nutren 1.5 (has no fiber ) or Jevity 1.5 (has fiber). It takes stomach weeks to adjust from regular diet to liquid diet.