Hello and welcome to HCM
in arm pit has nothing to do with your menstrual cycles.
There are many reasons for abscess in axilla
It could be due to lymphadenopathy
(increase in size of lymph node due to infection or inflammation) and subsequent rupture.
Various micro-organisms like bacteria, fungi and viruses can cause inflammation of the lymph node.
You need to get few investigations done.
First of all get a complete hemogram, fine needle aspiration cytology (FNAC) in case there is a lump in the axilla and culture studies of the pus discharged from the axilla.
This will determine the organism causing this problem.
Regarding your problem of irregular periods
, it is normal to have irregular cycles in initial years after menarche
due to irregular ovulation.
If the problem persists for longer time, you need to visit your gynaecologist. You mayb require some medication for a while.
Thanks and take care
Dr Shailja P Wahal