From your history I'm first thinking in terms of osteomyelitis
I'd advice you to consult an orthopedic surgeon to rule out it. Blood investigations, pus culture, X Ray
etc. may have to be done.
You have mentioned no history of trauma. And by the location of the swelling I am of the opinion that the etiology of osteomyelitis would most probably be tuberculosis
. If the diagnosis is TB you will have to take meditations for st least six months.
Only after ruling out osteomyelitis only I'd think of other causes like soft tissue
Wish your father good health.