First of all, take good care of yourself and find out the cause of your seemingly debilitating back pain. Can you do any type of physical activity and if you do, do any of them alleviate or exacerbate your back pain? It seems to be pretty rare for young person like you to have such severe back pain. You have ruled out sciatica?
I really hope other more experienced parents will chime in, I am tagging one of them @compmom. As a parent of a child who is really into music, my two-cents to him has always been not to be too narrow in his undergraduate study, set a broad foundation, after four years, if his music passsion is still there, then by all means give it a try. This might not be what you want to hear, but I just have seen/heard too many “starving musician” stories to feel it is a good idea to give up on your school now. Why not finish the last year, then pursue your music dream?
I am too conservative, I think the negatives more, maybe that is the baggage you have to carry once you become a parent.
Best of luck.