From what you have told me it would seem possible that you do have some sort of intolerance, but what concerns me (and I think is possibly a separate issue)  is the reaction you got when you ate the Pannetone. This reaction  seems more like a true allergy and if possible I think you should go carefully through what ingredients might have been in the pannetone that could have caused this. Talk to your GP about this as another time around a reaction can be  more  severe.

As for the wheat tntolerance (and it’s possible the two things are coexisting),  you could try investigating which foods might be upsetting you by keeping a diary of foods eaten and symptoms experienced,. However this may not be all that informative as sometimes the symptoms of an intolerance (tiredness, headaches, bloating as well as digestive upset) happen several hours or maybe even a day or two after eating the food.

If keeping a diary doesn't work, another option is to try the following bland diet  for a couple of weeks before slowly reintroducing foods:

Allowed

Meat, fish, soya products, all fruit except citrus, all vegetables except potatoes and sweet corn

Not Allowed

Dairy products, eggs, yeast, caffeine, nuts and alcohol. All cereal grains except rice.

After a fortnight, start reintroducing foods every few days (the one you will be most interested in is wheat, obviously), making a note of any symptoms that occur). You'll need to leave it a few days and should discuss your results with your GP.

If you are wheat intolerant, it’s likely that you will have a level of intake that you can tolerate without any problems, but this threshold is very individual and may even change over time. But the bottom line is that yes, you will need to find alternatives to wheat wherever possible. Fortunately supermarkets now do a large range of “free from” type foods which will help you no end!