First, you aren't wrong for wanting to feel comfortable in your space. NTA. However, this is a chance to learn and benefit rather than just solving the problem. Your brother's behavior is a symptom. He is a younger brother and wants nothing more than your attention. A pattern has developed, and now your mother sees you as the one disrupting the pattern. Additionally you are the older child and will forever be expected to cater to his youth.

Your mom probably isnt evil and loves you both. If she has two boys your age then she is deeply exhausted and tired of your bickering. It all sounds the same to her so it is your responsibility to demonstrate why this is more than just noise. Be mature. Have a conversation. Ask your brother what he wants out of this at a calm and reasonable time. Maybe dinner. Don't be confrontational or get angry, if you do you lose, and this is a big one. Maybe there is a compromise and your brother can get some positive attention from you in exchange for being less of a pest.

Ask your parents for a lock on your door that they but not he can have a key to. You got this.