Low fodmap/antihistamine diet
First thing is to cut out processed foods, sugars, antibiotics, hormones, chlorine, and fluoride.
Also cut out Caffeine, and eat plenty of veggies. Water is your friend and chicken bone broth does wonders. If you are a coffee drinker and it's difficult for you to quit then check out chicory root as a substitute. It actually has health benefits which you'll need in dealing with this problem. Probiotic yogurt is also a great addition. Make sure it's plain though. Hope this helps! There's more if you're interested, but this should give you a starting point.