6 week old kitten suddenly throwing up HELP I'M WORRIED !!!!!!!!?

My kitten is almost 6 weeks old. He was a stray. I took him to the vet, they checked him out, started him on a 2-dose only dewormer just in case... there was a mix up over the date of the next (orally given) deworm dose, and he got it 3 days early. They checked him for fleas, etc. said everything was fine. I've had him for 2 weeks now, he's usually completely healthy. For the past 5 days or so I've been letting him nibble on dry food, and giving him milk replacement formula, which he loves,and no wet food (which he had as soon as I got him until 5 days ago). He was completely fine when I went to bed, curled up next to me and fell asleep. Now I woke up at 4 in the morning to him meowing a kind of loud, squeaky meow. I noticed he was chewing on a wire. I picked him up and told him no and just pet him. then he moved to the edge of the bed and made a gag sound. I then saw there was white foam. Then I noticed before I woke up he must have thrown up...right by his litter box. A pretty decent amount. It's not really a foam it's just pure white (looks like the milk kind of) and has what I THINK are food chunks in it. I'm concerned about the possibility of having worms or some underlying infection the vet did not catch. Also, for the past five days I've been giving him the premade milk replacement formula, today I switched to a powder version I make with warm water...could this have been the cause for vomiting? even though it technically was the same thing? there was no problem with it for a week now.. could it be the food? which there was no problem with all of last week? I don't have anything around that he could have gotten into to make him sick that I'm aware of..I kitty-proofed my home. I'm really really scared, please help. One more question, what kind of a threat to humans does this vomit pose? I lysol-ed my bed (had white foam) and my floor (the real vomit with food)...do I need to do more or would this effectively kill anything like bacteria or worms?