Hello, Pain under the armpits is commonly due to muscle soreness, bacterial infection, lymphedema, lipoma, fibroadenoma, abscess or serious malignant diseases (tumor, cancer, etc). You are suggested to get clinically examined by a GP. Get blood workouts, routine tests, investigations and imaging tests done. The treating doctor may recommend you to get a biopsy done so that treatment can be started at the earliest. you will be treated accordingly. In the meantime, take food rich in anti-inflammatory property. You can also take analgesics to reduce pain and inflammation. Stay away from addictions if any. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Nupur K., General & Family Physician