Welcome to healthcare magic!
Your problem has many possible diagnoses- TB, local lymphadenitis
secondary to some infection in the arm, Lymphoma
, Hidradenitis suppurativa
The simplest way to get a confirm diagnosis is to take an aspiration sample from the lymph node.
You also need a physical examination by your physician and get base line investigations like Chest X Ray, Complete Blood Counts, Renal Function Test, Liver
Function Test, Ultrasound
Abdomen, Urine Compete Examination.
This work up is expected to detect the underlying problem so a definite treatment could be started.
I hope this advise would be helpful for you.
Still if you have any queries or doubts, please write me back,
I would be happy to solve them.
Wish you a great health!