Abdominal Swelling/Distension

Hello,

I am a 21 year old female and have been sufferring from abdominal distension for 3 years. I know that this is a common symptom however unlike many others that I have read, my distension never goes away when I am eating a normal, healthy diet (though I admit to the occasional but not overly often takeway). I have read that bloating often occurs in a routine such as people will get up in the morning and be flat but their stomach will increase during the day. To be honest, I look like I am pregnant all the time. The distension does not go away at all, never. Unless I go on a low carbohydrate diet which is fairly restrictive over 4 days. The distension is not the only symptom. With the distension/swelling, my weight will increase proportionally to the increase in abdominal girth so that my hip will increase by 14cm and my weight increases to up to 4kilos. I feel my rings are tighter, clothes that were loose on me are tighter my hips and thighs look and feel bigger. Yet this will all drop off in a matter of 3 to 4 days if I follow my strict diet. I have been told that it is "most likely IBS" but have no idea as none of the conventional treatments for IBS work (ie Buscopan, mintec, destressing etc). I do not have any diahhorea nor do I have constipation though sometimes after abstaining from carbohydrates my body needs to rush to the toilet once I ingest them again. I will swell up even if I eat a healthy meal of meat and vegetables. Foods that really trigger the swelling are potatoes, pasta, bread, softrdrink etc. I have been tested for celiac disease and it came back negative on the blood test and have been on the waiting list for a colonoscopy for quite some time. Please help as this problem just will not go away and like I said, my stomach is never flat while I eat healthy!!!