Thank you for the long advice!

I don't think he has worms, I would have noticed this as much as I have to clean his messes up. :/

I think all drugs have to be prescribed here, and I really don't wanna mess around with him, if I'm not sure what his problem is. It would probably be for the best if I took him to the vet, and I already would have wouldn't it be so damn expensive. :/ But I think I will (or send my mother do it since I'm moving away so soon and can't take him with me).
I really hope it's something as simple as the case you mentioned last! :)