That said, if I was in your position and if I couldn't tackle the problem in any of the standard ways, I'd take an NSAID like aspirin¹ on "cheat" days to temporarily suppress the immune system as an experiment and see how that works. I found a 1982 issue² of The Lancet where someone had the same idea and reports success with this strategy but I'm not even close to a medical professional and this is just one data point so YMMV, caveat emptor etc, etc.
---
¹But not ibuprofen or other NSAIDs, those seem to worsen the problem — https://www.thedailybeast.com/research-shows-link-between-ns.... Aspirin however has its own set of side-effects (bleeding risk, may interact with medication you are already taking etc) so strict diet is still the safest, long-term solution for now.
²http://sci-hub.tw/10.1016/s0140-6736(82)90024-1: 650mg Aspirin, 5-15 mins before meals, not after. Again, this is NOT medical advice, it is just one data point.
I've done elimination diets and had blood tests to determine foods I react to. I've also met with nutritionists to create meal plans. But over the long term I tend to gravitate back to foods that my family and friends tend to eat which includes stuff that jacks up my immune system (kid didn't finish her mac and cheese? I'm on it!...visit my Italian mom? pasta time!)
So how do you keep to what you know you should do when other people in your life are doing things to the contrary?