After so long on a LF diet, and then the antibiotics on top of that, you've likely really damaged your microbiome/gut. The LF diet was never intended for long-term use. A damaged microbiome is a really common root cause for HI, which you could possibly have. Getting off of the LF diet is not easy, though!
I don't think that adding in more restrictions (like low salicylate or low oxylate) is really the solution unless you're having reactions that you can directly tie to foods high in those things by keeping a food diary. Restricting more will only make it even harder to eat, stress you out more, and degrade your microbiome even more. Don't resort to just eating rice!
I was in the same situation last year: I went on LF because I was having SIBO-like symptoms but after 12 weeks I was so much worse and suddenly couldn't tolerate things I'd been fine with a few months before.
I decided to quilt LF so I used the plan in the book "Fiber Fueled", modified for histamine intake, and went from being able to tolerate zero FODMAPS to now eating as many as I'd like with nearly zero pain. It did take months to very, very slowly build things back up, but it worked. My guess is that even if your microbiome isn't the absolute solution to your issues, fixing it/making it stronger can only help. The book is by a GI doc and based in science. It is really helpful. He has done a lot of podcast guest spots if you want a TLDR of the book: he's been on the Plant Proof podcast several times and they're all good. He's also on Ep. 538 of the Rich Roll podcast, which is good too.
I still have histamine issues (my root cause was only partially my terrible microbiome), but they're better than they used to be and at least I can eat all the FODMAPS again so I'm not worrying about trying to juggle multiple restrictive diets.
So what you're trying to tell me is that an author, who is a *medical doctor*, who actually spent years and years of training, has a practice where he has helped sick people get well, has a best-selling book, and 4,482 reviews on Amazon with 4.7 out of 5 stars, is a quack? Am I correct?
Fiber Fueled: The Plant-Based Gut Health Program for Losing Weight, Restoring Your Health, and Optimizing Your Microbiome Kindle Edition
https://www.amazon.com/Fiber-Fueled-Plant-Based-Optimizing-Microbiome-ebook/dp/B07ZY7J2XW
by Will Bulsiewicz MD (Author)
4.7 out of 5 stars 4,482 ratings
Take a look at Fiber Fueled by Dr Will Bulsiewicz