Hi! We have a kitten named cosmo. We found it in a hole at 3 weeks old now it’s 8 weeks old. It’s always hungry and will keep eating as much as we give it. It also scratches and is always scared. Also I don’t know the breed.
Taking care of a kitten at 3 weeks old is very difficult, so nice work on getting Cosmo along this far. There is a general guide for taking care of kittens that can be found here: https://www.vetbabble.com/cats/getting-started-cats/how-to-care-for-a-kitten/
As for being hungry and scared, this could be a sign of many things or simply a behavioral issue. While a healthy appetite is generally a good thing, but I would definitely worry about internal parasites as most stray kittens have parasites of some kind. Toxocara cati is a type of roundworm which is very common as are tapeworms. I would recommend to have a veterinarian rule these things out first.
In the meantime, here is some additional information about deworming your cat: https://www.vetbabble.com/cats/health-cats/worms-in-cats/