Can a kitten just be generally sickly?

My kitten Archie reacted badly to his kitten jabs, and his limbs and jaw swelled up. He was kept in over night by the vet and he was fine afterwards. My mum bought a supermarket back of the neck wormer (bob martin?), and when we put it on him his neck went very red and scabbed over for a couple of days although he didnt seem to be in any pain. He'd recently got his kitten collar and he'd scratched at it in the way cats do. I was wondering if the collar had irritated the spot we'd put the wormer onto? He hasn't worn a collar since, but he is mircochipped. He's also a big strong kitten.
My problem is that he's getting s/n on monday, and I'm worried he'll react badly to the anaesthetic. My vet doing the s/n is the one who gave him his jabs so she knows he can react badly. He's still gonna get s/n I'd just like someone to put my mind at ease!

Get him to the vet immediately.
He's having a reaction to the toxins.
In the future, never, ever use flea/worm products from anywhere other than your vet.
They are quite deadly and have been known to kill cats and kittens.

He is not sickly just unlucky.Over the counter, medicated shampoos flea drops, flea collars etc should be avoided at all costs, unless your vet specifically recommends one. Collars are not necessary and are also a danger to small kittens (they are a choking hazard).

Depending on his immune system, how much colostrum he got from his mom, he could just be reactive to shots. The shots are usually three-ways and they use either a dead or live virus, depending on what the shot was. This is quite a load for a small kitten. Next time, just ask your vet to space out the shots. Also read up on VAS http://www.vas-awareness.org/OurCats.htm Not to freak you out, but it does happen, and recently it is happening more and more. Vaccinations are a personal choice, most people that I know around this area do not vaccinate their cats, or horses, but they do vaccinate their dogs.

Oh my god. That freaked me out. I had no idea so much could go wrong. And my vet gave it to him in the scruff of the neck! My poor baby!
He's not that small a kitten, 4.5 months and about 5lb.
The wormer was a couple of weeks ago, and he's since healed up. I'm never using non-vet approved products again. How are they allowed to sell these things?
So the s/n should be ok right? *hopes*