I have been haveing back pain for a year and no doctor knows why and it has gotten worse what can I do?

Work up. I would need to know more about your back pain before I can tell you what it is. I assume there has been work up done, so you will need to tell us the results of your xray or/and MRI if one been done. You may also have referred pain (pain that comes from the structures other than your back, such as kidneys or abdomen), so if not looked into, this may be the reason for not arriving at diagnosis.
2nd opinion. If a doctor has not been able to provide you with a satisfactory answer as to the cause of your back pain, it may be time to get another opinion and/or see a back specialist. Chronic back pain has a cause, it just needs to be found. Be sure to bring all prior studies and x-rays to the 2nd opinion doctor to limit duplication of work.