That just isn't possible, Finn. For a mother, it is never clean enough, it seems.. My mom bitches at me all the time because my bathroom isn't clean enough. "I worked on it for an hour!" I say in my defense. "I got everywhere, and everything!"
Her response: "Well, it isn't mom cleaned!"
What?! I just don't get it.. no matter how clean I think it is, she never thinks it's clean enough.. is there a manual to this machine called a mother?
To answer the OP: I'm not sure what you should do.. it sounds like we've ruled out the backyard, and cleaning your own room probably won't work either.. I would recommend that you hide your stash somewhere where you aren't going to clean, in other words, away from your room. I don't know how your house is set up, but I have a cache of places that I use as temporary spots: A grandmother clock in my living room(open the front, shove the diapers down to the bottom), behind our water heater(ours is downstairs, so I will hide things behind it occasionally), our storage room(it's outside, behind our house, don't know if you have one of those or not..). It's hard to say if any of these will work for you, but perhaps it gave you a few ideas? Only you know the layout of your house, and what's in it, so try to think of somewhere to hide your stuff where you won't have to clean. I do strongly recommend somewhere outside though..
Even though your mom, shockingly, doesn't seem to care about you using diapers, it's probably better for you to stop having your strash discovered. She may not care now, but if it keeps up, she may eventually say something to you about it. It's probably better to avoid that.
Whatever happens, good luck.