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.
Bring a pot of salted water to boil and fill a large bowl with ice cubes and water. Add the green beans to the boiling water and cook for 3 minutes. Using a slotted spoon or tongs, strain and transfer beans to the ice water. After 1 minute, drain into a colander and serve. If you would like to store your green beans for later use, you can prepare them for freezing.