it can be a swelling due to some underlying infection of the sweat gland as arm pits have a abundance of sweatglands whixh may get infected due to continuos friction of clothing. since how long have you has the swelling? is there any pus or blood discharge? taking antibiotics might not help as you need to know the exact cause of swelling You may schedule an online appointment for proper evaluation and management of your condition. Take Care.

Get it checked first dont take antibiotics by urself

According to your query and sign and  know about the disease and cause and it's best Treatment as you have mentioned as above . Please take consultation for better evaluation and best Treatment as it need complete history of patient as personal and family history. Please follow any medicine or advise after consultation only from a good doctor. Please follow good life style as • take plenty of fluid and • take less spicy and fatty foods • take home made food only and do exercise regularly with yoga and meditation  and please keep positive  attitude to fight any disease and any problem in of your life.

Need few more details Kindly consult

Can help you, kindly consult and provide detailed history for proper diagnosis and further management