Help! What's wrong with my kitten? He won't eat

We had a cat guest for about 9 days because his owner was traveling, and everything started from then
He would not eat his food whatever we put for him except for just a little every few hours

But then when the guest left, his food intake decreased more and he had soft poop, and so we took him to the vet, and he told us it was a cold and gave us medecine

At that time we would mix canned food(it was the first time for him to eat that) with his usual chicken or beef meals, and we would grind everything so that it becomes easier to eat.
And he would eat that if not from the plate, we hand fed him
So after the 3 days of the prescribed medecine we took him back to the vet for a check up and the cold was gone
But at that time he would sleep all day and was a bit limp, but was eating fine, so vet told us that this would go away after 3 days, and it did!

He was fine for about 4 days after that, then he started walking away from his food, and no matter what we put for him he just sniffs it and walks away, except for the cheese he loves and when we put him canned food on its own
And sometimes eats a bit of the raw chicken thighs and he would eat the cooked chicken if he got really hungry

And now for two days he really won't eat anything we put for him except for the stuff mentioned above, but now everything he eats is really small portioned, and walks away from everything else even if he is really hungry

He poops and pees normally, but he has been pooping everyday instead of once each 2 days
He sleeps a lot, but when he wakes up he plays like crazy
And he has become more affectionate than before
So what could be wrong with him?????? I don't know what to do anymore :'(
Should I take him to the vet again? Or would this resolve on its own?

And I forgot to mention, he is 5 months old, we still didn't give him his rabies vaccine, but he took the first one at 3 months old, and he isn't neutered

What tests (if any) were run on him?
That he acts hunger but won't eat much makes me think he is nauseated.
Also, exactly how much is he eating: is he losing weight? I ask only because you mention he is pooping every day instead of once every two days. If he isn't eating much he should be pooping much.
His hormones could be ranging too; he's that age.
So, I would take him back to the vet (a feline specialist if there is one near where you live) for more blood work. Once he is well, I would get him neutered.

It's kind of hard to tell it sounds like he's eating but only eating what he wants to eat?

Has your kitty lost any weight? Is he gaining weight?

The stress of a guest could cause a cold and cause him to go off food so that's normal.

Some kitties are snackers, they just want a nibble here and there all day long vs a meal. 

Honestly it kind of sounds like he's holding out for the good food. He knows you'll give in and give him the yummy stuff as long as he holds out.

He's probably missing his owner. What was he eating before staying with you?

The vet only used the stethoscope to determine that he had a cold, no blood work done
And he is losing a bit of weight

And the guest has left about 3 weeks ago, so I don't know if he's still worried till now

And he has always been a picky eater, but he usually would only eat when he's hungry
And I forgot to mention above, he's got a kind of fungus on his mouth, he had this before and we treat it with a gel the vet prescribed before
And also we suspect he has ringworm, there's a hairless part near his ear, and he hurt this part before
Could these be a factor of why he won't eat also?

So I've decided to take him to the vet tomorrow inshallah
But if vet says he's fine, and he continues this with the food, what should I do?
And thanks a lot for your answers[emoji]128522[/emoji]

I'm sorry I misunderstood your first post and thought the cat was the guest cat. 

Maybe the fungus in his mouth making him uncomfortable?