Well I say this because when my brothers were kittens I tried them on adult food which I had leftover from feeding ferals and it gave them wind and I could tell they had indigestion. But this was dried food.
Nothing wrong with you. I have 2 rescue cats, one tom and one female. The 18 month whimpy tom lost his bro 8 months ago so I got a 3 yo female for company for him. He eats like a pig and she goes in and out of the catflap all day. She is a whinger and wakes me up outside my bedroom door howling...
The thing about adult food is it's harder for a kitten to digest and well make it fart because of this and cause digestive problems. Having said that I had a kitten grow up with me in 1951 and as we were poor we fed it scraps and not cat food. It was healthy and lived till 17.
I had spaghetti bog 2 days ago but too much sauce so tonight I'll have the rest of the meat sauce, add some kidney beans and chilli and have chilli con carne with rice. Lots of chilli.
Okay, if you're not joking then applying a flea treatment is the best option. Flea collars don't work, the parasites need to be killed and collars don't do this. Fleas lay there eggs in furniture and bedding and carpets and hatch at different times so eradicating them takes a while. If flea...
Ham sandwich on ciabatta for lunch and beef stroganoff for dinner but using milk thickened with flour instead of sour cream due to too much cholesterol.
As already mentioned it could be worms. If you can't afford a vet at least give pussy a worm pill, the one for roundworm as this won't do any harm anyway.
Some cats are just scaredy cats. My two ginger brothers are different insomuch as one is frightened of his own shadow and the other is totally the opposite and I've brought them up exactly the same. So I have to be extra gently and coaxing with the timid one.
Try stroking them all at the same time together to demonstrate you love them all equally. Cats, like dogs, are prone to the green envy syndrome so the other two might be worried you don't love them as much and are jealous.