You can never completely prevent them from going in your room, but you can live in ways that make them think they have no need to go in there. Keep your room clean, don't leave dirty clothes / dishes laying around, wash your sheets, empty the trash. Also don't behave in any ways that make them think you're up to something. For example, don't smoke or do drugs or any other behavior that makes them think they need to go snooping around for "evidence".
As for your diapers, if you use disposables, don't keep the wet / poopy ones around. If you use cloth, wash them often. When I lived with my parents, my mother only went snooping around once. I'd made myself a pair of "training pants" by taking about four pairs of white jockey shorts, putting them inside of each other and sewing them together. It was summer, nobody else was home, and I'd spent the entire day wearing them, wetting them, wearing them until they dried, wetting them again, etc. By the end of the day the smelled really intense (something that I love, by the way) and I took them off and put them in my closet, figuring I'd wash them the next day when my parents were at work.
I went out for a while and came home and my mother was standing there holding them between her thumb and forefinger and asked "Are these yours?" Apparently she smelled the pee odor and went looking for the source and found them. I got really embarrassed then angry about this. She later apologized for invading my privacy, said "if you have a problem and need to go to the doctor, let me know." I told her I didn't. I never heard another word about it (but from that point on I was very very careful to not ever get caught again).