Hello Good evening,
According to your description, it is look like
furuncle or boil.
But due to chronic infection, might be
fibrosis developed there, and it converted in to lump with pus.
It commonly due to infection of hair follicle or
sebaceous gland caused by some types of bacteria, nothing to worry so hard.
But you are giving history of months now, so you should go to surgeon, who will do I & D (
Incision and Drainage) for it and followed by some antibiotics and analgesics, which also acts as anti-inflammatory.
It may be needed Biopsy, if your surgeon think so.
Regards,
Dr. Naresh Jain