Remeber saw some TV commericals about some drugs handling "Gas". Probably you can ask the staff in shoppersdrugmart. Just tell them you need something for stamache gas. They can help you out.
Sometime, it's the result of pressure. If you encounter a lot of pressure or you feel depress recently, it may help to make your stomach uncomfortable. Medicine can only solve the symptom, to resolve the cause, you need to find by yourself, to find some changes in your life routine that may cause the problem.