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 large pot of water to boiling. Allow 1 gallon of water per pound of green beans. Fill a large bowl with ice water. Working in batches, carefully lower the green beans into the boiling water. Boil small beans for 2 minutes, medium beans for 3 minutes, and large beans for 4 minutes.