Could be Irritable Bowel Syndrome but lots of things to consider:
swallowing air - caused by chewing gum, eating too quickly, drinking through a straw or sports bottle, habit, fizzy drinks.
food intolerance - keep a diary and see if you can identify triggers.
diet foods and drinks - many of these contain sorbitol (even the sugar free gum) and this will cause bloating and diarrhoea.
It could equally be because you are not eating enough. Malnutrition can give you a bloated stomach, especially if you are severely lacking protein. It is a condition called kwashiorkor and is often seen in the third world starving.
So lots of suggestions, but impossible to give a definite without knowing a lot more about you.