I am not espetially good at coding but I'd say I'm a fine artist and a decent musician, I really want to make a game but I have no real motivation.

My recommendation is to start with something small. Even a mini-game that is well-polished can have its appeal.

If you doubt your own motivation, I suggest you do this: do any activities not related to video games at all for couple hours or a day then ask yourself: do you want to make a game or not?

If the answer is no, then maybe you shouldn't make a game at all. But if the answer is yes, then get started with something small.