Thank you all for all of your advice. Things are going much better. I think I did just need to wait a little bit longer, because his symptoms got a lot better. He didn't have any reactions to adding stuff back in, but since I added wheat back, he has had a little more gas (but no mucous or blood), so I'm taking it slow (only eating it about once a week) and may end up cutting it out again if it looks like it's getting worse.
Again, thanks for all your advice!