Will someone give me some advice?

Here's my problem, my brother keeps on letting my dirty, nasty dog onto my bed whenever my mom is at work and my dog is'nt allowed inside but my brother does it behind her back. Anyways, I pretty sure my dog just got fleas and my brother once again let my dog on my bed, whatever i do i just cant stop my brother from doing this and im afraid to tell my mom because she yells at my brother really really bad if she finds out that he's been bothering me and i kinda feel a little sorry for him when she yells at him, and also if i do tell on my brother im pretty sure that he's gonna be calling me a tattle teller for the rest of my life. He's like one year older than me and he thinks he's the boss of me just because of that but for some reason i still feel bad for him sometimes. And since my dog has been all over my bed i decided to leave them on the floor to wash for later and use other clean ones and my mom is yelling at me, and she's telling me that all i have to do is just shake my bed sheets off and it'll be clean but she doesnt know about my dog getting on my bed. And she's not letting me wash my sheets, and i really really need help, because i dont know what to do now, and i just need soem advice on what to do. Should i tell my mom? I really dont know what to do, and it'll really mean a lot of someone helped me out :'(