Have you ever got to the root of what is causing it?
I was like you, slim everywhere else but had a big stomach which made me very self conscious as it made me look pregnant when I wasn't.
First of all I went to the GP for tests to rule out cancer of the uterus, a known cause of bloating.
When I had the all clear I went on an elimination diet, taking out gluten, etc one by one to see if that made a difference.
I found alcohol and eating a lot of sunflower and pumpkin seeds and too much stodge or carbs of any type made me bloat so I restricted them.
I then took up running and pilates, swimming and concentrated on removing inflammation from my diet so took out as much as possible, any thing processed and or with added sugar.
I finally got rid of my large tummy by going on a 3 day fast ( keeping up my fluids with coffee, marmite stock, green tea infused with slices of ginger).
Now I regularly practice intermittent fasting and the big tummy has finally gone
My diet is now predominantly a small bowl daily of leafy green veg, nuts and seeds, all kinds of fresh fruit and veg, tinned fish, and sourdough bread, butter, different types of Japanese food and Asian food such as homemade Dal soup, different cheeses and lots of eggs.
Not only am I fitter and leaner, I also have tons of energy and my protruding tummy a thing of the past :)