Need half with leaving 15 week puppy alone.

So two weeks ago my puppy became super clingy, ever since I can’t even go upstairs to the bathroom without him crying let alone leaving him at home.

I’ve been trying to very very slowly increasing absences, desensitising my approaching the stairs ex but nothing seems to help.

The thing is as well, on a night he’ll go int his create by himself and lay down no issues with me going up to bed.

I really don’t understand it, I don’t know why he got clingy out of nowhere.

Any advice would be appreciated