Plumsmom, thanks, I'll try. He can be a picky little bugger. I gave him sweet potato and broccoli chop this morning, with a little seed mixed in. He seems to be eating it but he might just be trying to pick the seeds. He's a junk food junkie. I'm glad he's eating at all, the vet said he might not have much of an appetite.
Clark, cool, thanks! I tried to read up on it but most of what I found just said don't give onion ever, so I was pretty freaked out.
So update this morning, he seems pretty much fine. Eating well, still very kissy, still stinky but not as bad. Yesterday, it reminded me of my restaurant days, when I'd open a bin of sliced onions that were a couple of days old. Today it's much lighter. His poo seems normal, maybe a little darker than usual but only slightly.
I'm a natural worrier, I get it from my mom, so I'll still be keeping an eye on him, but it helps to hear that he'll probably be okay from folks here in addition to the vet. Thanks again, everyone. <3