Sharing a bathroom!

I'm 14 years old and I share a bathroom with my 10 year old brother. First of all I'd like to say that I don't have a lock on my bedroom door and I'm not allowed to have a lock on my door. Whenever I ask my mom just says, "You don't need one, what do you need to be lockin' your door for?" What am I supposed to say? To masturbate. Anyways, I have to go to the bathroom to masturbate where there is a lock on the door. And I have to shave in there, and do my makeup and hair in there, and have my period in there, and be naked and shower in there. And I can't do all of this with my little bro knocking on the door. Plus my mom always asks why the door is locked and she makes me let my brother in whenever, so I have to just get dressed and go somewhere else if he needs to take a shower. Ugh, am I over reacting? Or is it normal to be annoyed?