I would second going back to school if you can afford it. You can always start going part-time and then transition to full time if you really see it as another

I would second going back to school if you can afford it. You can always start going part-time and then transition to full time if you really see it as another career path. I'd also recommend the Art of Problem Solving's Calculus text, it has a solution book, as well as their Volume 2 book. Try working through those on your own, since you have great background in math you should find it quite enjoyable, and perhaps somewhat challenging.