What Causes Visible And Tender Spot On Mid Spine?
Muscle issue most likely.
Detailed Answer:
I read your question carefully and I understand your concern.
I am assuming that the manifestations are limited to the spot you describe without any symptoms like pain distributing in the lower limb, trouble with bladder control, fever etc, issues which might raise the red flag of a compression of the nerve root or spinal cord, infections and so on. Also you say there is nothing visible and I suppose nothing on palpation to suggest a cyst, enlarged lymph gland etc.
So in this case I believe the most likely cause would be a muscular issue such as a pulled muscle. In that case it is not something to worry about, simply avoid exertions and it should gradually disappear over the course of some weeks.
I remain at your disposal for other questions.
Read below.
Detailed Answer:
Thank you for the additional info.
I would still not exclude a muscle strain as it may take longer at times.
However that length of persistence does call attention for the possibility of a rheumatological problem like intervertebral disc disease or arthritic changes of the spine at that level. I would say a simple x-ray to exclude urgent issues like fractures, sliding of the vertebrae as well as to show arthritic changes would be a good cheap first test. In terms of treatment only physical therapy to strengthen back muscles and an over the counter pain killer would be needed. If x-ray inconclusive and symptoms persist a MRI may be scheduled.
One other possibility would be fibromyalgia which typically presents with such tenderness, but usually involves more sensitive areas, not the single one.
Let me know if I can further assist you