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.
Fresh, young beans should be able to cook up perfectly well in less than 6 minutes. Tough old beans, you'll have to cook a lot longer to get them tender. Look for beans that easily snap in half when you bend them. 1 pound fresh green beans, ends snipped off and discarded, extra long beans, cut in half if you want.