You can have a pinched muscle in your back putting pressure on the nerve going to your stomach area. That pressure can make the organs in that part of the body react in different ways, pain being one of them. Here is how you can release those muscles:
Back:
Place your left hand on your left knee. Place your right hand over your left shoulder and with your fingertips find the muscle next to your spine. Press on it and hold. Relax, take a deep breath and exhale and don’t tense up any part of your body. After about 30 seconds there should be a release happening and when it does slowly lower yourself forward onto your right leg. If you can lean over the outside edge of your leg it will be better for your release. Continue holding for a total of one minute. Then release but rest your body there for one minute longer. Then reverse and do the right side.