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The picture is suggestive of problem of spine or urinary tract
It is rather intriguing that no cause was found in spite of of so many investigations...
Unintentional weight loss
of more than 10 Kg is a serious matter / and is an indication for more investigations...
You may need colonoscopy
Some investigations may have to be repeated after some time.
You need continued follow up
Getting admitted to a Multi-Speciality tertiary care Hospital (all under one roof) - may be a better idea...to find the elusive cause.
Wishing speedy recovery