I want to teach myself some of the undergraduate courses so I can skip ahead, but without having the commitment of school with its time and money investment I lack the motivation to do so. I know I can as during my free time in high school I taught myself how to photoshop, but that was easier because I was locked in school and I had clear goals in mind with what I wanted to do in Photoshop; I wanted my image to look x way and kept googling how to do that until my goal was realized.

While I enjoy doing math and physics, I don't particularly have a related goal in mind, by calculating the trajectory of an asteroid I don't gain any immediately useful thing, while learning how to do x in Photoshop I gain a cool image.