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.
Boil the green beans and then turn the heat on low. Cover the saucepan with a lid and leave it to simmer for about 10 to 12 minutes. Use a strainer to drain the green beans from the water, but put some of the cooked/boiled water on the side. Use a blender or food processor to puree the green beans.