The cyst in your underarm can be a simple bacterial infection of the hair follicle or it can be a part of an inflammatory disease known as hidradinitis suppurutiva. Proper examination of current lesions and present of any scars along with history of previous similar eruptions and history of any treatment taken. Please consult a qualified dermatologist directly or you can consult online. Dr Nikhil Kajale is a good dermatologist in Nashik. You can meet him. Hope this is helpful.