My mum gives me no privacy whatsoever to me apart from in bathroom!?

You will have to be firm but polite with her by saying to her about what she is doing, and give it to her straight, ask her out right "Why are you being this way with me, i have ask you please don't come into my room, as i am not doing anything wrong, nor am i hiding anything" if that does not work then if possible get a lock with a key on your door, and just tell her that if she keeps coming into your room and doing all the stuff she has been doing then you will lock your door, as i had to do that a few years ago when i had my brother staying at my house, as he would go into our rooms (That is mine and my children's) when we went out and would touch things and we knew it was him, it may have been a bit dramatic but it kept him out, hope you find a way of keeping her out and giving you the privacy you want.