I keep getting rejected from jobs

I (F16) did my NPLQ 10 qualification a few months ago and passed. Since then I have applied to multiple lifeguard jobs at different pools and gotten rejected after the interviews. I am feeling really discouraged as I know a lot of people my age who immediately got jobs easily after doing theirs. I don’t think it’s an availability thing bc they were all part time or zero hours contracts. I did receive minimal feedback from one of the interviews and they basically said it was bad but I don’t know why. I felt as if I had answered all the questions properly.

Pls could I have tips for my interviews in the future?