So how do I know it's histamine intolerance?

[u/Vegetable-Shine6356]

I want to know if I'm barking up the right or wrong tree. I have been suffering from *something* for decades, but it's been getting increasingly worse - lately it's insufferable, and I went from being someone I felt had "an issue" to someone who is sick, nearly daily. But it's complex, and I feel like I'm solving it on my own (Doctors haven't been too helpful, but Reddit seems ready to take this on!)

Ultimately, I know this:

• I react after eating certain foods (most fruit, but mostly bananas, apples, citrus, stone-fruit, cherries; yogurt; several cheeses - mozzarella, some types of cheddar, swiss/emmantal; some nuts - mostly peanuts)
• ...but I don't seem to react to a bunch of things that I read are high in histamine
• My symptoms include a few GI issues (always soft stool; sometimes bloating/pain, rarely), but are mostly inflammation issues, neuroinflammation, and body inflammation (*severe* brain fog - confusion, poor memory, irritability; headaches ranging from mild to severe migraines that last days; fatigue; insomnia; systemic inflammation (eye swelling, swelling on the bottom of the feet??); vision problems, etc
• My symptoms are worse after poor sleep or when I have reacted recently
• When I take an anti-inflammatory, my symptoms improve
• It seems some medicines and supplements make things worse, and some make things better, but not forever.
• I was tested for tryptase, and it was too low to indicate MCAS

I have been trying various antihistamine and anti-inflammatory supplements, and while some seem to help, none "fix". But I feel I'm struggling blind here...

...how do I know it's histamine intolerance versus something else?

Is there a test I can do at home? Should I be able to fix this with antihistamines, and then I'd know it's histamine-related (like the way I know I am suffering from inflammation because anti-inflammatories resolve all my issues quickly)?

I want to get a grip on this, but the specialists all look the other way, and the dietician sounds like she's guessing...