Stomach feels like its sucking up under ribs when standing up breathing

[poddyk]

My stomach feels like it is sucking up under my ribs when I am standing up when I breathe. When I am lying down or sitting it feels normal when I am breathing but as soon as I stand up it feels like my stomach is pushing up under my ribs and I can't get a deep breath, like my air is cut off. I can put my hand on my stomach and push it in when I stand and I can breath fine but as soon as I let go I can't hardly breathe. What would cause this??