First I must apologize for neglecting you for so long. I've been suffering from a severe backache that my doctor was having difficulty diagnosing. After more x-rays, I was diagnosed with osteoporosis compression. This compression causes tiny fractures and that's where the pain comes from.

According to Orthogate:

Compression fractures are the most common type of fracture affecting the spine. A compression fracture of a spine bone (vertebra) causes the bone to collapse in height.

Compression fractures are commonly the result of osteoporosis. About 700,000 cases of compression fractures due to osteoporosis occur each year in the United States. Spine bones that are weakened from osteoporosis may become unable to support normal stress and pressure. As a result, something as simple as coughing, twisting, or lifting can cause a vertebra to fracture.

One of the causes listed is coughing and I had a bout of bronchitis when my back pain started.

I'm now on a strong pain killer and, although I can still feel a dull, throbbing pain, at least I can function again.