Try working on the assumption that you have a gluten intolerance. While you wait to see the doctor, keep a food diary listing what you eat, when, and what symptoms you had. Try to modify what you eat to head towards making your own meals from scratch. So roast your own chicken, don't buy it pre-cooked. Use cooked rice in your stuffing instead of breadcrumbs. Boost your fibre intake - I pre-cook brown rice in te microwave (it needs to simmer for twice as long as white, that's all) and keep it cooked in the fridge fora few days. I then microwave just the little bit I want for each meal.
Metamucil - husband used to take the plain one, hewas told that if you mix it in milk Occupational Therapist (OT) takes like a vanilla smoothie. But these days he takes plain psyllium and stirs it into fruit juice of his choice. It's cheaper and has fewer additives.
I can't tolerate psyllium at all, I get your symptoms. I get the same ones with rolled oats, so I have to invent my own oat-free muesli. I substitute puffed brown rice for oats.
Gluten sneaks into a surprising range of foods - a young friend who has coeliac (extreme gluten intolerance) ate a caramel her cousin offered her, and got violent pain. Turned out there was a trace of gluten in the caramel. So be careful - you need to use as much food made yourself from raw materials, as possible. Instead of using packet dried herbs, for instance, use fresh from your garden. Buy raw vegetables and fresh meat and cook up a casserole yourself. Thicken stews with cornstarch (make sure it is CORN cornstarch, not wheaten) or arrowroot. Or use potato flour, or just whole potato cooked to a pulp, that will thicken a soup or stew.
Check out Healthful Living forum too. It's not just for dieters.
Marg