My 4-month-old appears absolutely miserable anytime I give him rice cereal or oatmeal. Should I try something else?
The American Academy of Pediatrics and virtually all other experts advise against introducing solids before 6 months of age, so I'd wait awhile before giving him any more. (Babies are not meant to digest solids at 4 months, as you have observed.) When you do offer solids again, start with small amounts of fruits and vegetables, such as applesauce, pureed carrots, smashed pears or sweet potatoes; try them for a few weeks or more before offering oatmeal or cereal grains. I think these varieties of simple carbohydrates are easier to digest than cereal grains, which have a little more protein and require a bit more "intestinal work."
By the way, unless your baby has shown allergic tendencies, I don't think you need to wait three days before introducing new fruits and vegetables.