It is probably too late for you to see this but you need to see a sports doctor or orthopedist right away. There's a good chance that you have Spondylolysis. That means you probably have a stress fracture in your back. Football and pitching both lead to Spondylolysis. About 1 out of every 2 teenagers that go to the doctor with lower back pain turn out to have Spondylolysis.
The treatment isn't that bad. Generally it is just rest and in some cases they'll have you wear a brace to protect your back.