He's not very happy and probably a bit lost after the cage clean. A full cage clean removes all their scent. They leave scent trails all over the cage to find their way around (they don't see well) and also to mark it as their territory. If it all smells unfamiliar and something or someone has "raided" his cage he may also be a bit scared and not feel safe.
So tips people usually find help is - only do partial cage cleans. Don't clean everything at the same time
It really helps them settle and feel less stressed by cage cleans.
The way to make it easier for you and for him is to have a lot more substrate in the cage (this actually works out cheaper with partial cleans and spot cleaning). The bottom half stays clean and dry and when you change the substrate next time you replace half the old substrate and mix it in with the new - so it still smells familiar.
When you do the substrate, don't clean anything else. Do the wheel a different week and any other items a different week again. Our human instinct is to clean everything all at the same time so it's all clean! But for the hamster this is like being thrown out into the street! All unfamiliar and not homey any more.
As he's only been with you two weeks then it's probably a major upheaval for him. Maybe put a smelly treat inside his house (eg a tiny bit of cheese) and he'll start using it again.
Having said all that - if the weather is very warm they often do sleep out in the open to try and cool down.
He won't be happy with just a thin layer of shavings though - they like to burrow down in bedding and bury their hoards. So you need at least 4 to 6" deep of substrate. If you get a large bag it works out cheaper. So the base is almost full to the brim. He'll probably be a lot happier with that.
If you could add some more you can mix the existing shavings in with it so it smells familiar.
Also after a cage clean I scatter food and hide special treats in different places, to distract them out of it.
Hope he comes round soon. I always say sorry if I've upset them! They hear your tone of voice and may forgive you!