It could be many things. It could be from slouching or sitting in a way that is causing the diaphragm to be compressed. Do not try to over straighten, just think of relaxing the muscles and allowing yourself to fall into a natural position. It could be injury from working out and doing crunches or other movements. It could be a stomach ulcer.
Another option is to blanch green beans quickly. Blanch your green beans by boiling them for 3 or 4 minutes. This removes the skin of your green beans. You want your beans to be somewhat tender, yet have a little bit of crispness to them. Determine the crispness, by how long you boil them.
Plunge the green beans into a large quantity of ice-cold water (I keep adding more ice to it). A good rule of thumb: Cool for the same amount of time as the blanch step. For instance, if you blanch sweet green beans for 7 minutes, then cool in ice water for 7 minutes. Drain thoroughly.