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.
Add water to your steamer and bring it to boil. Put green beans on the insert, and steam. The time for steaming green beans really depends on what you are planning on doing with the green beans later. If you are just going to dress them and eat it, you may want to steam the green beans longer, 7-8 minutes. If you want to stir fry them afterwards, 3-5 minutes should be enough.