From personal experience I can sympathise having shared your symptoms.
After nearly three years of trying many suggestions I have now have found that by removing dairy and yeast from my diet, the symptoms you describe have now gone. Literally overnight I felt the improvement. Dairy was a big change, but yeast is even bigger and took a great deal of effort, as all food now has to be prepared from scratch. As others have said' keep a food diary'.. Record every single thing you eat and drink, also write the time down of when you ate it. Record when you feel unwell and you will soon see a pattern develop.