Are you living on a **** set? Or at Wayne Manor?

not quite sure what your living situation is

Lock. The. Door! Seriously, at least in the USA I thought most bedrooms had a lock. Even if there is an emergency key above the doorframe (there often is), you will hear the person fumbling with the door before they can enter - giving you time to warn the person that you are not ready for visitors in your room. If this has happened more than once, I suspect that it’s not entirely an “accident”. You either need to make sure your door has a lock and use it or move somewhere else. And by the way nearly anyone with a screwdriver can install a doorknob with a lock - just go to your nearest big box hardware store. It doesn’t require drilling any new holes and much in the way of mechanical or carpentry skills. Doorknobs and latches are standardized so replacement is easy and the instructions are on the packaging. Just do it with no one else around and use one that resembles the original - Then if they make an issue of the change you will know that none of these intrusions were “accidental”. Oh by the way, if the door swings in to open you can get a rubber door wedge to jam under the door that makes it very difficult to open while requiring no tools or modifications or special skills. Also check for a hidden surveillance camera in your room…

Maybe lock the door when you’re naked?

Why don't you lock the door?