Severe back pain, what is it from?

Yes you should go back to the doctor. It could just be growing pains or you could have an old injury that hasn't healed right. I got into a car accident when I was 16 years old and I have nerve damage in nerves in my spine that go to my neck into my legs which makes not only my back hurt, but my neck and legs as well. I also have three fractured vertebraes and knee problems as well. I hope you find out the cause of your problems. Back pain is the WORSE also is knee pain. My doctor only gave me pain killers. I could have surgery but it is too risky because the problems are on my spine and doctors do not like to do surgery too close to the spine because too many problems can come up, like something going wrong, and me ending up paralyzed.