Brief Answer:
Read below.

Detailed Answer:
I read your question carefully and I am sorry about the state you are in.

While it might have been useful if you had uploaded the full report of the bone scan in the report section, from what you report the issue is a problem of the sacroiliac joint or a fracture of the sacrum. It is a cause of debilitating pain which can be dificult to treat, persist for many months and at times develop into chronic symptoms.

As for the cause, often it may be in the setting of a rheumatological condition like rheumatoid arthritis, lupus etc. I do not know whether you have had any blood tests for those. If not some screening tests for inflammation, rheumatoid factor, antinuclear antibodies are recommended.
Other causes may include trauma, some sports putting too much stress, non correct walking posture, hormonal factors especially in women as hormonal changes due to life events like pregnancy lead to changes in joints which loosen up and are more susceptible to wear and tear over the years.

In terms of OTC medication you seem to be already under maximum dosages. Medication for chronic pain like amitriptyline, duloxetine, pregabalin may alleviate the symptoms.
If those do not help at all, then perhaps injections must be considered which may include cortisone injections to reduce inflammation, local anesthetics. They effect may be limited to some months but by allowing better physical therapy exercises might prevent recurrences.

I remain at your disposal for other questions.

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