Re: reflux back or is it teething...or the flu???
I don't know that you can sort out what's going on with your LO based on the data you have. But the fact that your LO has a fever, a booger-y cold, stinky diapers, isn't as interested in solids as usual, and seems tired and uncomfortable makes me think he's got some sort of a bug. An allergy doesn't fit with what you describe, especially considering the relatively sudden onset.
You're doing exactly what you should be doing to get him well: nurse, nurse, nurse! There's nothing better when baby isn't feeling well. Even if he throws up 5 minutes after he nursed, he will still get hydration and nutrients from the milk. It digests fast!
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"