[Yes I've posted this question before but I think in the wrong category]

I have a fairly flat stomach, but every time after I eat, my stomach bloats up and gives me a small pot belly. Then it reduces again with time and when I’m hungry again my tummy is flat again. It doesn’t hurt or anything, it’s just bloody annoying.

[Background]
I have a spastic colon.
I’m not allergic to anything that I know of.
When I was younger I did a lot more exercise so I used to have a flat tight stomach. But these muscles aren’t tight anymore due to me being lazy.
This happens WHENEVER and WHATEVER I eat. Not just certain foods. Nor does it matter how much I eat, although the more I eat, the more bloated.

If someone could please explain the theory behind this, why does it happen. And then a possible solution?

Thanks