This is the 11634th most frequent Russian word.
желудке
"Желудке" is the prepositional case form of "желудок," meaning "stomach."
Here, 'желудке' refers to the anatomical stomach and is used in a locative sense to indicate where the pain is occurring.
У меня болит в желудке.
I have a pain in my stomach.
In this sentence, 'желудке' again refers to the anatomical stomach and indicates the place where the digestion is happening.
Еда в моём желудке переваривается.
The food in my stomach is being digested.
Here, 'желудке' refers to the feeling or symptom within the anatomical stomach after eating.