I agree with the above posters: find out the cause of your back pain. I know this is more challenging that it may seem. If it is your SI joint, look into PRP, or platelet rich plasma, a newish procedure that can work wonders. Have you had an MRI? Keep looking for the right doctor. A rehab doctor or physiatrist might be a good choice.
As for schooling, you have finished two years, right? Have you finished gen eds?
Is it possible to take a leave- or withdraw- after this semester (assuming it is not possible to withdraw from this semester, though that might be even better).
I think you need to regroup and look at the big picture, and think about ways to accomplish what you want in terms of studies, music and work.
Do you need to go to a conservatory or school of music? If so, perhaps the best route is to have a teacher, practice and audition for grad school.
There are many ways to finish a BA, and there are schools that will take 65 transfer credits, 90 transfer credits. You could do a degree completion, adult learner, distance learning (online or low residency). or continuing ed program (these mainly differ in name only) and, say, take two classes at a time while working on piano. I know many dancers who do p/t school in order to have a degree once they stop dancing or while they dance and have a day job.
Or, could you stay where you are and switch majors to a BA in music? Or another major that you would like more (humanities?) while studying piano on the side.
There are many paths you can take but clearly you need to get off the path you are one. And you probably need to rehab your transcript so to speak.
This may also sound off the wall but you could look into the possibility that you have ADHD. An inability to do work that doesn’t truly interest you, paired with an ability to sort of hyperfocus on something that you are interested in, can sometimes be a sign of that. And that could be a helpful direction with some remedies.
I would say finish a bachelor’s at your current school, perhaps majoring in music, OR withdraw and finish in a non-traditional way. No matter what you choose, get that back diagnosed. And get back to piano.
Finally there are many ways to have music and piano in your life, professional and amateur, performing and teaching. Think about that too, and perhaps what kind of day job you could tolerate too!