I'd suggest, before you go gluten free, get a blood test for celiac antibodies. I believe they do 2 tests. Very simple blood draw. That way, if you show the antibodies, you'll KNOW you have it. Others have recommended a stool test for gluten. I don't know about it; some say it's the most reliable. A dr. may advise you to get an intestinal biopsy. You should check that our for yourself - but from what I've read, they take snips from your small intestine (which is 20 feet long) - looking for patches of inflammation. There's a good chance they could just get patches from healthy areas and miss diseased patches - so I wouldn't say it's the "gold standard" they claim. Plus it's an invasive procedure with risks.
If you test positive you probably need to see a doctor and make sure you aren't malnourished - you may need lots of supplements - because we tend to not absorb things easily. Celiacs often have brittle bones and vitamin deficiencies. There's also a certain type of rash that some people get called dematitis herpetiformis - you can google and find photos of that online. Also, many symptoms overlap with fibro. Some people have IBS; some have joint pain. If you have celiac, it will set you up for many different diseases as you get older. The good news is it is SO treatable! Just quit gluten.
There are a lot of posts on here about gluten. You can google that - or celiac disease. Celiac is the most severe form of gluten sensitivity, which can range from mild to severe - and which can be triggered at any age. There is a genetic profile that runs in families - and it's often found in those with northern European, Scandinavian and British blood. But anyone can have it. You can google the Celiac Sprue Association and also, read the celiac forums.
To stop eating gluten, you have to stop eating cereal grains: wheat, barley, rye (and probably oats), as well as things like spelt and triticale. Because most flour is made from wheat, you usually can't have any kind of cake, pie, cheesecake, donut, bread, pasta, breakfast cereal, etc. Nothing made of regular flour from any of these cereal grains. Also, no beer or malt products.
To be safe, I stay away from all CEREAL grains except rice. I can have corn and tapioca, and flours made from those things, as well as potato flour. That leaves everything else in the food supply that you CAN have. Meat, fruit, veggies, dairy (tho some have lactose problems), eggs, jello, nuts, applesauce, sugar, honey… basically, it's a healthy diet. You should supplement with fiber though, since you aren't getting it from the grains. I use something called FiberSmart - made of organic flax fiber with some other supplements in it. I also take probiotics. And I buy whey protein powder and make protein shakes.
The tricky thing about gluten is that it is found in just about everything processed and packaged - you have to learn to read every label. You now can buy some packaged foods without gluten. But most soups, frozen dinners, canned foods, etc. have it. Most condiments, dressings, sauces, etc. have it. Gluten is used as a thickener and most of us are trained to like the texture and taste of it - so you might miss it until you get it out of your body. That takes about 4 months. Gluten is also used in a lot of medications as a filler, so I have to ask my pharmacist to make sure a drug is gluten free. If I'm buying something over the counter, and can't figure it out, I whip out my cel and call the company.
I believe there is a list of ingredients that you should question at the Celiac Sprue Foundation. Things like "hydrolyzed vegetable protein" or "modified food starch" - you have to call the company and ask them what the source of these things is. Most soy sauce is made from wheat, though you can buy brands that are not. That means no more Chinese food. If you are out at restaurants, some of them are good about gluten free menus - but not many yet. Some say they are gluten free, and then serve you food with bread on top of it! This probably won't bother people who are mildly sensitive - you can just take the bread off. But I'm very sensitive - and if my food is contaminated, it makes me sick - I get increased neuralgia type pain.
As to the all or nothing question - I don't know the answer. I know some celiacs who eat pizza (wheat crust!). My feeling is, after reading about all the diseases gluten problems can cause, I'd rather avoid it entirely. I guess you have to listen to your own body and see what you can tolerate.
Hope this answers your questions! This is what I've learned by researching, but there may be new information or changes - so I suggest you get a good book on it. I really liked the book "Dangerous Grains." There is an enormous list of conditions in the back that are related to gluten sensitivity. The diet is not hard, once you learn it. But it is hard to go out to other places and eat regular food - you have to ask questions about what's in it.