A Gluten free diet should not be commenced until after a diagnosis of celiac disease has been confirmed by a qualified Medical Practitioner.
This procedure will involve a number of tests, which may include blood tests and an endoscopy.
Sometimes when all the symptoms are leading to the assumption of gluten intolerance and you feel like you can no longer bear to continue eating a normal (gluten containing) diet, it is easy to jump straight onto a gluten free diet. Remember if a gluten free diet is started prior to having an endoscopy or blood test, this may interfere with an accurate diagnosis; thus possibly giving you a false negative result.
The best piece of advice to consider is: if you feel you have the symptoms of celiac disease, go to the doctors without delay. If you have been following a gluten free diet without a diagnosis, it would be suggested to discuss this with your doctor.
It would be necessary to return to a diet containing gluten for a period of time before any tests were undertaken. It may be hard to eat gluten (again) as this is likely to make the symptoms return, however it is really the only way to be 100% sure if your problem is actually celiac disease or maybe just an allergy to wheat.
Lets face it - changing over to a gluten free diet from a normal diet is a life-time commitment. It will take a lot of discipline to maintain a strict gluten free diet when you are use to eating "anything and everything". This new gluten free diet is also going to be costly - so being confident of the diagnosis will give the strength and perseverance needed to embark on the gluten free journey.
It may be helpful to seek help from a dietician. A dietician will be able to help you initially with what you can safely eat and what amounts should be eaten. This will assist with maintaining a healthy weight range ensuring adequate nutrition is achieved.