Kitten not eating much and sleeping a lot

I have a 6-8 week old kitten named Kirby. My boyfriend and I found an add on Craigslist about kittens free to a good home. We met the woman who seemed very nice and well-kept and brought him home. When he got here he made himself right at home. Running around, playing with everything. We got him loads of toys and he would play with them forever. She said he was eating dry food, so we started him with one can of wet food and transitioned him to kitten dry food which he seemed to eat fine.

It's now two weeks later and I started noticing him dry heaving, as if he was trying to cough up a hair ball. I was of course alarmed so I called a vet. She said to bring him in because they don't see hair balls in kittens that young. We took him to an emergency animal hospital because he had seemed to stop wanting to eat or drink. (Still being playful and cuddly, purring like crazy) the vet did some blood work and said everything looked normal and sent us home with an appetite stimulant and a de wormer.
The appetite stimulant didn't do much of anything. He seems uninterested in food. I got him to eat a little bit of tuna yesterday and last night we gave him the de wormer. It was a liquid tube we applied to the back of his neck. He began to get very tired and started salivating.
He also had a small amount of diarrhea which were all side effect symptoms I read online.
He is drinking water today; urinating fine and eliminating fine. Just still very tired and not interested in food.
He is very cuddly and purring constantly.
I am beside myself. I am so worried and panicking over every little thing. I want to take him back to the vet but it's so expensive and don't want to panic or overreact if I shouldn't be. I just need some advice. He looks completely normal, no sneezing or coughing, his eyes are fine no watering or crustiness... No worms seem to have been in his poop. No big feeling belly.

Any suggestions? I love Kirby so much I'm a nervous wreck.

By the way he is a black and grey tiger kitten.

Hi and welcome to the site

Sorry you are having problems with your new kitten.
It does sound like he's had a reaction to the dewormer.

You could just ring the vet and ask for advise over the phone without taking him in

I'm worried about the not eating - you really need to get food into him. Try anything, chicken, cheese to get him started. Cats can't go long without food before it's starts other serious health problems.

But just to put your mind at ease, I would ring the vet and ask for advise over the phone

Thank you! Was not sure if the de wormer would make him not hungry or what? I put down some milk, some wet food, some tuna in water, he goes up to it like he is going to eat it, but as soon as I touches his mouth or make he just backs up and begins licking his lips. The vet said the only other thing to do is an X-ray? I'm just confused it doesn't seem like a blockage being he is using the bathroom. I just want him to feel better.. He is sleeping on my face right now

Touches his mouth or nose **

Hmmm..... He's licking his lips because he feel sick. Diarrhea usually happens with partial blockages of the intestine but it is possible for it to happen with total blockages. If your cat has diarrhea with a total blockage it is usually due to the water in his system that made it pass the blockage before it became a total blockage.

Does that require surgery?

Just an update: Kirby drank some milk and started munching on a little bit of his dry food earlier. Also very playful and ate a treat for
Me when I came home from work! Still a little diarrhea, I am hoping he will go back to normal!!!!!!!

Glad to hear he ate a bit.    Maybe try something like Cat Sip(Petco sells)instead of milk?    He may have trouble digesting milk which would contribute to diarrhea or upset tummy.

Get kitty off of cow's milk. KMR or even lactose-free 2% milk might be better for Kirby than milk. Please keep us updated.