Have you considered the possibility of gut dysbiosis? That is when your gut's "good bacteria" get overtaken by bad guys. It can result from infection, poor diet, or antibiotic treatment.
The gold standard test would be a complete stool sample analysis -- a CSA. They look for the bad guys, incl. parasites (more common that you'd think; often acquired camping or doing water sports, or from pets), as well quantifying your "good bugs."
IME, the most common causes of gas & bloating are: 1) a habit of swallowing air, common in gum-chewers. The gas is "clean." 2) dysbiosis, as above, but the gas is often unpleasant. 3) food intolerance, with gas going either way.
Food intolerance may not show up on an allergy test. There are many people who know they get gas/bloating from certain foods, and who test negative for food allergy. Sometimes it's a matter of keeping a food journal/log, or of dietary elim & challenge. But perhaps you already went this route with the nutritionist. Common offenders are lactose, dairy intol, and gluten intol. But it could be anything ...
A specialist may have something to offer you, a med to try to reduce the symptoms.
Hi Dizzy, I've been having the same problem. I've suffered with IBS for over 10 years but lately, the past 5 months or so its at a point where I'm bloated and swollen and gassy all the time!! Its terrible. I too thought it was food allergies because there are certain things I eat that I know cause that in me, but I've kept a journal and tried to eliminate certain things only to still ahve that problem, tried lactaid, gas-x and other herbal supplements but nothing causes relief. I'm trying some new medication so we'll see if that works, but its a terrible feeling. Especially because I can't seem to even wear normal clothes anymore because I will bloat so bad I look like I'm 9 months pregnant. I feel for you and with you the best!!