Ask HN: Where/How to start re-learning math?

I am 23, and have not actively engaged in mathematics since I was 14, I enjoy programming but I am at the point where I can no longer avoid more in depth concepts which directly require, to a degree, mathematical fluency.

Math was incredibly easy for me at 14, so I figured it would always be easy, even if I never took another math class. I was wrong, and I would appreciate any advice, as I would like to keep diving into more and more difficult and complex programming-solveable challenges.