'Works of art' VS 'artworks'

[First post here!]

So, what is the plural form of artwork? Am I right in thinking simply adding 'S' to it is wrong, because it sounds wrong in my head, at least. Can someone therefor please explain, using the best terminology and accuracy as possible, why 'artworks' is wrong and why 'works of art' is right.

I know art can't be countable, but I thought work can't be either. Yet in the case of 'works of art' it is used as something countable..

I was trying to think of it in the case of 'flock of sheep' and 'array of colours' but I'm not even sure if you can have a 'sheep flock' and 'colour array' or 'flocks of sheep' and 'arrays of colour'.

I just feel a bit stupid not being able to work this out myself blush

Much appreciated for a reply!