Thank you for your query at DoctorSpring.com
I understand your concern.
I see that you have a boil under under your armpit. Boil or furuncle is an infection of hair follicle. It is most commonly caused by bacteria called as staphyloccocal aureus. Small boils burst and get drained on its own. But in your case it looks big to me and being in sensitive area of armpit it may cause a lot of pain. I would advice you to get it drained by a physician. He might also do your physical examination to check if you have boils in other parts of your body. Recurrent boils are common in diabetes, poor health. So, please get your blood sugar level checked.
If the boil bursts on its own wash it with some antibacterial soap till all pus is gone and apply antibiotic oinment and bandage. You can take acetphenomen for pain relief.
Prevent occurent for future boils by maintaing good hygine and staying fit and healthy.
Hope this was helpful,
Please feel free to discuss further,