It's normal for your stomach to swell and flatten in a cycle, as the food and drink you consume reaches your gut (also called the gastrointestinal tract) and is digested. This activity contributes to a daily pattern that shouldn't normally cause you discomfort or pain.
This is a companion discussion topic for the original article at https://patient.info/news-and-features/why-does-my-stomach-bloat-in-hot-weather