I note you say you have had this problem for a 5 year duration.
I note also all the remedies you have tried & your visits to dermatologists'. However, there is no record of what medications they have prescribed.
Dermatology is a visual subject & the diagnosis & thereby the treatment depends on a good visual & would be nice if you could upload a clear digital image of the region.
From your description, it does seem to be reflective of a condition called Confluent & Reticulate Hyperpigmentation
of Gougerout -Blum. This is of course an off-the-cuff diagnosis & a skin biopsy
to confirm it may be in order. It could just be a case of a simple Pityriasis
Versicolor fungal infection
Both are easily treated with a visit to the dermatologist & a systemic antifungal in a single 400mg dose of fluconazole
may be effective. If in Bangalore, you are most welcome to come over & consult. If in the North, this young dermatologist named Kalpana Pathak seems a good bet!
Good Luck & Godspeed!
Dr Praveen Rodrigues MD
Dermatologist, Cosmetologist, Venereologist
Vikram Hospital & St Martha's Hospital, Bangalore, India