I'm not a doctor, but there are a few possible explanations for side stomach pain when squeezing a bump under your arm. One possibility is that the bump is a swollen lymph node. Lymph nodes are part of the body's immune system and can become enlarged and tender when fighting an infection. Swollen lymph nodes can sometimes cause referred pain, meaning that the pain can be felt in a different location from the source of the problem. Another possibility is that the pain is unrelated to the bump, and instead it may be caused by strained or pulled muscles in the side of your stomach. It's always a good idea to consult a healthcare professional to receive an accurate diagnosis and appropriate treatment.
