My Left Side Of My Abdomen Has Been Swollen And

my left side of my abdomen has been swollen and buldging out even having movement with it. it feels like a baby is moving around inside of me like its doing flips and trying to push its way out of my stomach but im not pregnant i have had multiple blood and urine tests and they all came back negative. it gets so swollen to where it feels like my stomach is going tear open and explode. iv been pooping its not like im constipated. i went to the hospital but my stomach wasnt swelling while i was there, it seems like when i stand up or move around is when it starts to get big and bulge out but since no signs were showing at the hospital they just diagnosed me with insomnia and bloating. i really would like an ultra sound to see whats actually going on in there but im scared that it could be ulcers or maybe the begging of my appendix bursting or even an ectopic pregnancy. idk im scared and have been getting panic attacks over it and its hard to sleep. iv also been losing weight. im 20 years old female and im pretty underweight even though i eat normally im only 69 pounds and at 5'1'' im really scared and would like answers but it seems like the doctors think im crazy. please help!