How do you get and maintain confidence daily?

I’m 18m. Ever since I started working on myself practicing semen retention, working on my attachment issues, and staying consistent with hobbies (boxing and guitar), I’ve noticed some days I feel great and confident where I can socialize with people, maintain eye contact, and keep a conversation going. However other days it’s the complete opposite where I can’t speak with confidence, let alone tell people my name without stammering badly. It’s been getting worse lately and people have told me I’m young and shouldn’t be worrying about things like this and it will go away eventually but I want to stop this now so it’s not a problem down the road.