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
a muscle strain or spasm.
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.