How do i fix my lower stomach bloating?

I'm 19, 5'5 and 125 pounds. my stomach has been consistently hard and bloated every day since i was in 6th grade. I'm toned everywhere except my lower stomach. i have abs on my upper abdomen, but as soon as you go below my belly button, there is a large "pudge" that protrudes. it is NOT fat. i have been to tons of doctors and had tons of tests done, all of which came back with no results. no hernias, cysts, celiac's disease, chrone's, ibs....anything you can think of...i dont have. ive also been on diet and exercise plans...all to no avail. (ive tried cutting out sugar, gluten, wheat, dairy, meat, and just about anything else you can think of for a month...this was also unhelpful) its extremely uncomfortable (constantly feels like my stomach is going to explode out of my skin) and i cant stand it anymore. i feel like a prisoner in my own body. please help.