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.
Place green beans in a large skillet; pour in 1/4 cup water. Bring to a boil over high heat. As soon as water comes to a boil, cover pan and cook 3 minutes. Uncover pan, and stir in butter. Cook 1 minute or until water evaporates and beans are crisp-tender. Sprinkle beans with salt and pepper.