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.
While the beans are cooking, peel a center strip from each new potato with a potato peeler (it makes them look fancier). At the end of 30 minutes, add the potatoes and onion to the beans; add 1/4 cup more broth, if needed. Cook, covered tightly, until potatoes are tender, about 25 to 30 minutes. Check the pot often to make sure a small amount of liquid remains. When the potatoes are tender, tilt the lid slightly, off to the side of the pot, and continue to cook until the green beans are completely wilted, about 15 minutes.