My hobby has a very frequent disease that is stomachache and mucus in stool (means once in a couple of months, in winter season, when place changes)?

Irritable bowel. The colon is lined with goblet cells which produce mucus if irritated or inflamed. Periodic abdominal pain and mucus is common in irritable bowel syndrome(ibs) as long as there is no blood seen. Change in diet, season, travel, stress can cause irritable bowel syndrome. Abdominal pain is also a common symptom of as long as the is no red flags i.e. Weight loss, rectal bleeding, vomiting or fever.