Iron deficiency anaemia can lead to organ damage

Surprisingly, most people do not pay heed to the early symptoms of an anaemic condition. Even -, like decreased energy, pale skin, shortness of breath, palpitations or irregular heartbeats, weakness and light-headedness. They seem to be minor ailments curable with a temporary rest. But they could lead to organs being damaged in whole or in parts and pave the way for the onset of an acute anaemic condition. Extreme case of anaemia can cause chest pain, angina and heart attack. Other extreme cases could be jaundice, spleen enlargement, dizziness and fainting spells. — Dr B Sesikeran MD, Former Director, National Institute of Nutrition, Hyderabad 

It is a transient problem, going by your description. It may be a manifestation of premenstrual tension. However, pain in the armpit is a rare variant. Most often, women experience some breast pain during the time of their periods. In your case it could be a case of a breast tissue in the armpit. I suggest you meet a gynaecologist, who would examine how much of breast tissue is extending to the armpit. — Dr Rajapriya Ayyappan, Gynaecologist, Om fertility centre, Srinivas Priya Hospital, Perambur