Sometimes i would be confident based on my looks, athletic ability, or how good i am doing in a certain social situation, but i want to know how to stay confident and positive?

These people that have great frame and great confidence, where does that come from? I want an unshakeable frame and high confidence. I think i am pretty great but i also suffer from some negative thought patterns. I am too emotional and i sway between happy and confident and sad and depressed

EDIT: A little backstory if any extra info is needed. In high school i was very confident and outgoing, played sports etc. but ever since i graduated i also find it a little hard to be as confident? Or it could possibly be i dont have as much social proof now that i dont play sports