I'm in a similar situation but a decade older. My "aha" moment came with Ivan Savov's "No Bullshit Guide to Math & Physics". For some reason working through this book "sticks" in a way that Khan Academy and similar online tools haven't. That, combined with randomly reading entries in "Mathematics 1001" have gotten me to where I can read through audio acoustics/DSP and information theory papers (my main area of interest) and understand what's going on.
https://books.google.com/books/about/Mathematics_1001.html?i...