This is difficult for me to deal with.  B complex is what stands between me and migraines.  Whenever I stop B for just a few days, I get a migraine.  All my adult life I would get a violent migraine for 3 days like clockwork until a doctor told me to try B complex and it worked.  The only time I get a migraine is when I've run out of B.  This has worked for me for over 15 years.  I am soon to be 79.   My cardiologist has me stop all vitamins for about 3 days and I always have a migraine when I go in for the bloodwork.   D level is nearly at optimal.  I don't take A, I get enough from food.   What a dilemma!

I think the best approach is to lean how to read product labels, especially the allergen warnings, and these lists might be helpful:      

It looks like you are referring to this product: https://shop.kingarthurbaking.com/items/gluten-free-bread-flour Their site says: "Made with gluten-free wheat starch to give baked goods incredible taste and texture, it’s ideal for classic yeasted recipes like artisan boules, bagels, cinnamon rolls, and burger buns", and it is true that Codex quality wheat starch is gluten-free, and does make better baked goods. However, it also contains very low levels of gluten (under 20ppm), and some celiacs do react to this level, so if you are super sensitive it's best to avoid it. They also make this very similar product, which doesn't include any wheat ingredient, and is certified gluten-free: https://shop.kingarthurbaking.com/items/gluten-free-bread-flour Although labeling products in the USA as "gluten-free" that contain such wheat starch is relatively new, it has been offered in Europe for decades. You can read more about studies on it here: https://www.celiac.com/celiac-disease/miscellaneous-information-on-celiac-disease/gluten-free-diet-celiac-disease-amp-codex-alimentarius-wheat-starch/

Our Functional Medicine doctor has always ordered the Spectracell Test for Micronutrient Deficiencies.  It tests the intracellular levels of the nutrients, not blood levels.  When high dose, targeted supplementation did not resolve the deficiencies after retesting at 6 months and then a year, he ordered genetic tests.  I have a genetic inability to process Vitamin D, B12 and antioxidants, so I am on high doses of those for life.  The rest of the initial deficiencies resolved within 6 months to a year and a good multi vitamin is sufficient to address those.  My husband has historically had high homocysteine levels and his low folate, B 12 and B6  levels are because of his MTHFR gene mutation.  Always good to get to the root cause!

Welcome to the forum, @Idnam! Ranitidine and Famotidine are not proton pump inhibitors. They are H2 blockers. It is true that histamine intolerance is common in the celiac population. We often don't produce enough of a histamine regulator called DAO (diamine oxidase). Not sure, but this may be due to damage to the gut lining by celiac inflammation. You might also want to research MCAS (Mast Cell Activation Syndrome) as it is often goes hand in glove with histamine intolerance and is actually the root cause. Or, at least that is my understanding. By the way, you can purchase DAO capsules but there is not clear evidence they work.