Welcome and thanks for posting your query to HCM.
After reading your query I can make out that your arm pit has infection of either oil gland with hair root or the sweat gland
. Because of the infection there is oozing of whitish pus and scab of black color.
For the betterment kindly do not try to pinch or squeeze the swelling.
Do warm water compresses over the area.
Wear cotton clothes and cotton undergarments.
Stay away from hot and humid environment.
Apply a cream containing Mupirocin
or fucidin in it.
You can take oral antibiotics
containing amoxcycillin or cefadroxil
under medical advice
With good health wishes
Dr. Sanjay Kumar Kanodia