It seems that due to continuous sitting for 8 hours it affects your digestive system giving rise to this problem.
Some times chronic gastro-intestinal infection does give rise to this problem.
Go for ofloxacilin, tinidazole
combination medicine course for 3-5 days.
Go for abdominal muscle exercise daily.
Go for physical exercise like running, walking, swimming.
Avoid more tea or coffee and junk food.
Ok and take care.