Another with Crohn’s here (20 years) a bit exasperated at the inaccuracies, sweeping statements and doubting of the OP on this thread.
Crohn’s is a strange condition and still lots not known about it, symptoms and flare triggers can often be quite personal to the individual.
Personally I find that when my disease is well controlled through medication I can pretty much eat what I want with no consequence (although still need to be a bit careful with alcohol and very rich food eg creamy sauces - but they’re not great for anyone really!). But when I’m in a flare I find food can absolutely affect symptoms, and I err more towards plain foods eg plainly cooked fish and rice, which I think is similar to FODMAP.
Exclusion diet was also suggested to me when first diagnosed, although actually I think there’s emerging evidence that a more balanced Mediterranean style diet is good for Crohn’s - but perhaps trickier when in flare. Basically I’m saying let’s not doubt the OP! And colonoscopy can reach the start of the small bowel (terminal ileum). I should know, I had one yesterday and saw the start of my small bowel on the screen! And I was given a preliminary diagnosis during colonoscopy too, rather than waiting for biopsy results.
But, OP, I would definitely echo what other posters have said about trying to get back to your doctor for some more advice on medication - or perhaps they are waiting for biopsies to review this? I’d try to see hospital rather than GP - but presumably you are now under outpatient care? Is there an IBD nurse team at the hospital you went to? If so I’d definitely suggest contacting them as they’re normally fantastic and can be a good bridge to the doctors too. And Crohn’s & Colitis UK have loads of useful advice and support.
Finally as others have said sadly I don’t think it’s fair to be upset with family members for enjoying food you can’t eat, but if it’s part of a broader pattern of feeling unsupported I get why you might feel that way.
Good luck!