I agree with the others on here, you need to go back to the doctor!
As others have said, If you stopped eating gluten before the test it would not work, or if you were not eating enough gluten.This applies to the blood test and the endoscopy. There is also a gene test but not widely available. There is a second blood test you can have, but that would not work if no gluten in the diet. One week may not be enough, I think 6 weeks is recommended.
Coeliac disease can start later in life, triggers are not understood. The good news with coeliac is you can get well by changing your diet !
Sometimes coeliacs are also dairy intolerant but this can improve once they have been on gluten free diet for a while.
I hope you get sorted out soon, it sounds to me that the blood test was not correct as you were not correctly advised that you should eat sufficient gluten prior to the tests.
IMHO your symptoms after eating gluten are very dramatic and you should go back to the doctor to discuss what to do next. It is a difficult situation because you have to eat the gluten for the test to work, but the gluten is making you ill.
As others have said, if you keep a food and symptoms diary it may help convince doctor you are coeliac without the tests, or at least get a referral to gastroenterologist, who may diagnose on the basis of symptoms rather than the tests.
You should check the Coeliac UK website, and you could phone their helpline. Don't be fobbed off, from what you say in your post it's likely you are coeliac but you should not be too worried, apparently so is Novak Djockovic and he just won Wimbledon! (He says 'gluten-intolerant' but it amounts to the same thing.)
If it turns out you are not coeliac then the doctor should investigate other causes, but if you are coeliac the good news is that you will probably make a good recovery and be able to stay active once properly diagnosed and following the diet.
My brother is keen cyclist and has always eaten very healthy diet. He had great difficulty getting diagnosed as he appeared in good health.
It's best to get a diagnosis rather than going it alone as they can also test for related problems such as early signs of osteoporisis, which can be treated, and aneamia, and you can get prescriptions for gluten free bread, pasta and flour, which is otherwise very expensive.