I’m not sure how old you, and I’m going to guess you’re female and that you’re a teenager. Am I right? ❓
It’s understandable that you’re disappointed that your mother is not behaving the way you want her to, but rather than try and make her be something or someone she’s not (imagine if the tables were turned!), find someone else to talk about sex with. Not everyone is going to be as comfortable as you are talking about sex, and none of us pick our parents so being disappointed in family members is pretty normal, but something you have to get over.
See if your father will talk to you, or if not, an older sibling or an aunt or some other female family member. It would be nice if our parents were always everything we wanted, but the reality is when disappointed, there are often other people we can forge relationships with to expand our family and get what we need.
I hope that helps! 🙂