It seems that you are having chronic omphalitis
The skin of umbilicus
In your case it occurs of and on.
Your blood should be tested for DM,HIV
or any immunocompromised conditions.
Pus from umbilicus may be tested for bacteria and its culture and sensitivity test.
And accordingly , antibiotic may be taken.
Anti inflammatory drug is also taken.
Immunobusters may be taken to improve the immunity.
However, you consult dermatologist
I hope you got my answer.
Dr. Ilyas Patel MD