Based on your answers, some of the most likely causes of your back pain include
degenerative joint disease (also called osteoarthritis)
disk disease
sciatica
spinal stenosis
muscle spasm or strain
Less likely is a fracture (as may occur with osteoporosis or slippage of one vertebra on the one above or below it). It's also possible that you have some combination of these or a rarer cause of back pain.
While over-the-counter pain medicines, a heating pad, and rest (balanced with activity) may be helpful, it is important that you see your physician to evaluate these symptoms, especially if you are not improving over a number of weeks.