I know it's not going to be terribly productive to start blindly eliminating more foods but I'm having an overwhelming tomato suspicion at the moment. Over a year ago Roo wasn't eating much tomato...perhaps here and there. That could explain the "clean" scope. These days he's a regular ketchup lover and has recently taken to those luscious little rubies otherwise known as grape tomatoes.
Tonight, while dipping his fingers into ketchup and licking his fingers, I swear he got a little rash on each cheek. It was slight and Mufasa wasn't here to verify, but it was there. And it hadn't been there a minute ago. It eventually went away but then he threw up tonight after dinner. This one seemed like a clear reaction to something...no oral delay or gag to speak of. So, I'm left wondering. Maybe it's the tomatoes. Then again, patch testing to tomatoes was negative so...ugh.