Do you think i should get a bathroom for myself?

Well, I share a bathroom with my sister. She's really messy with it.

First, she leaves all of her clothes in it when she's done in the bathroom.

Also, there's toothpaste all over the sink. There's even some on the walls! (no kidding!)

There's...

also something in the tiles of the floor where the toilet plunger is...

And she always steals my deodorant, and uses the whole thing up in about a few days!

Whenever I try cleaning the bathroom, it ends up getting the way it began within a few days. I ask my parents if I can use their bathroom, but they always say, Use your own, it's your problem that it's messy.

Should I get a bathroom of my own?

LOL, well, doesnt sound like its going to be too easy to just get one of your own. Your sister sounds exactly like one of my daughters, and you sound like the other one. The messy one is now grown up and on her own, and I tell you, the problem has just become worse... When I go to her house, there is NOTHING that will make me use her bathroom. She doesn't care and she doesn't get it. Her husband is amazingly just the same as her.

I don't envy you and I don't even have a solution. I expect your parents will just want the two of you to sort it out between yourselves and that really is the best way... Is she older or younger? Do you have anything she needs/wants/borrows? You need to be in a position to use some leverage over her, lol. Negotiation is needed!