Thanks for your query .
I would be pleased to answer your question .
This sounds very much like a furuncle
. You seem to be having a bacterial carrier state in the arm pits and hence you get recurrent infection episodes after shaving.
I would suggest you to apply mupirocin
cream in the arms for 3 days after shaving .
For the present condition , you should take an oral course of antibiotic to heal it faster .
You can take paracetamol
once in case of pain .
Thanks and Take care