Back pain on the lower right side. pain radiating down right buttock and leg. what could it be?

You have sciatica.: Sorry you are suffering from this...There are several common causes of sciatica ranging from sacroiliac to irritation of the spinal nerves from a herniated disk. If your pain does not get better, if numbness affects the crotch, or if you have bowel or bladder difficulty then you need a surgical evaluation, otherwise your primary care provider can take care of getting your sciatica to cool down.