F44 128lbs no negative health history except acid reflux, pain below sternum which stopped after 2 wks of omeprazole with every meal two weeks ago, and episodes where an area the size of my fist located under my ribs, rt side medial feels like it expands then typically with 3 rhythmic pulses, contracts a little more with each pulse until it is normal again. It s frankly, freaking me out. What could cause this?