My wife says to mention kitty will also likely need to be wormed. Eating fleas will lead to worms and cats do tend to lick them up when bathing. :-/
Shoot...the problem is likely you've given kitten an overdose of pesticide. I'm not sure what you mean by sweaty (cats don't sweat) but if it's what I think your describing, then this is probably the problem.
I would suggest a vet visit to be sure, but at the very least hold off on the flea collar and baths for a while. 12 weeks is VERY young to be wearing a collar.
i'd also keep kitty separated from those kittens. It sounds like they aren't caring for them properly and you don't want kitty to pick up any illnesses (if it isn't too late). fleas and kittens can be hard to deal with, especially if there's no mother cat around. generally using a flea comb and powdering the bedding areas can take care of the situation, especially if you can keep the room temperature cool (fleas THRIVE in summer).
Keep in mind there are other possibilites for what can be wrong. You don't mention how you got this catl. If it is a stray, you should take it in immediately, as 3 months is right about the time when FeLuk hits and begins it's first symptomatic attack, which can be deadly. The symptoms you're describing could very well be that as well.
Good luck, let us know what happens.