Have you spoken to any clinicians about this?
Eating vegetables and lean protein is basically the best way to feel full, according to satiety research (i.e. research into 'feeling full for longer'). If you're unable to get much veg in your diet because of some reason, that could well make a big difference.
Other than that, I'm a firm believer in the idea that people who have tried and failed to lose weight need talking therapy, which focuses on REBT/CBT. This was my case - I was obese class III a few years ago, now obese class I, and on my way to being 'only' overweight. Bear in mind that I've always had a decent level of physical activity - for years I've gone on 2-3 day hiking trips, cycled 125mi charity bike rides, spent my free time running around after cub scouts on camp wide games, cycled to work, etc. I needed to understand the reasons I was eating more before I could address the behaviour. Simple example - when I grew up, it was a single parent household, my mum worked 3 jobs to feed us, and we weren't allowed to leave the table until we'd finished our plate. This has baked into me a mentality of I must always empty my plate else it's wasted food. But in reality, this isn't true most of the time - if I'm full, I should stop eating, and not force myself to eat more. Yes we should of course encourage that extra mouthful of veg if a child hasn't touched their veg, and we shouldn't give ice cream and chocolate puddings if they barely touch their tea, but that's a bit different. I hadn't ever thought about this until a discussion with a therapist (who I wasn't even seeing because of my weight) My partner I know will often eat treats quite quickly because when she was younger, if you left sweets or chocolate hanging around the house for too long, somebody else would eat them.
The other big thing for me was making gradual changes, rather than drastically changing my diet overnight.
Fundamentally people know what they need to do to lose weight - eat fruit/veg, lean meats, avoid processed foods, and do some exercise. Everything else is tinkering around the edges frankly.
Yet many (most?) people who want to lose weight do try quite hard, but ultimately don't succeed, suggesting it's not merely a question of what should I eat, but why do I eat what I currently eat and don't eat what I don't eat.
Your case may well be a bit different in that if your body really does react badly to vegetable fibre, you might need support from a qualified dietician (note: not a nutritionist, who are not necessarily qualified).