Why do I have constant cavities?

I got my first cavity filled a year ago and now I recently seen that I have 2 cavities in my back two teeth on the same side! I recently just got my braces off so now I'm extra careful. My mom has very bad teeth. Her teeth are all fake and I take most of her genes in personality and look wise.Then I look at my brother and he has perfect teeth! I floss everyday, brush day and then at night, and mouthwash. I don't get it! I do not drink soda, chew gum rarely, or anything sugar. I look at my brother and he drinks soda and sugar ALL THE TIME and still has no cavities! Why am I so prone? I'm 14 btw!