I don't see how cornstarch could alter the test results. Where did you read that?

For pain relief I take a combination of Thiamine (Benfotiamine), Pyridoxine B 6, and Cobalamine B12.  The combination of these three vitamins has analgesic effects.  I have back pain and this really works.  The B vitamins are water soluble and easily excreted.   Hope this helps!  Keep us posted on your results!

Welcome to the forum, @Xravith. I experienced similar symptoms before my diagnosis.  Mine were due to the loss of vitamins and minerals, essential nutrients we must get from our food.  With Celiac Disease, the intestinal lining, made up of thousands of villi, gets damaged and cannot absorb essential vitamins and minerals, especially the eight B vitamins.  The loss of Thiamine B 1 can cause muscle loss, inability to gain weight, edema (swelling), fatigue, migraines and palpitations.  Low thiamine can cause Gastrointestinal Beriberi with symptoms of nausea, abdominal pain and bloating.   Thiamine is only stored for a couple of weeks, so if you don't absorb enough from food daily, as the thiamine deficiency worsens physical symptoms gradually worsen.  If you're eating lots of carbs (like gluten containing foods usually do), you need more thiamine to process them (called high calorie malnutrition).  Thiamine works with all the other B vitamins, so if you're low in one, you're probably getting low in the others, too, and minerals like iron, magnesium, zinc, and calcium, as well as Vitamin D..  Talk to your doctor about checking for nutritional deficiencies.  Most doctors rarely recognize vitamin deficiency symptoms, especially in thiamine. Get a DNA test to see if you carry any Celiac genes.  If you do not have genetic markers for Celiac, it's probably IBS.  If you do have genetic markers for Celiac, it's probably Celiac.  I was misdiagnosed with IBS for years before my Celiac diagnosis.   Keep us posted on your progress. P. S. Deficiency in thiamine can cause false negatives on antibody tests, as can diabetes and anemia.  

No she didn't because if I want to ask I have to pay 700$ for 1 hour appointment so I couldn't even ask. I read that fillers like cornstash can alter the result and tylenol contains it so that's why I tried to find someone who can answer. 

Did the GI doc give you any rational for stopping the Tylenol during the gluten challenge? I have never heard of this before and I can't imagine a good reason for it. Ibuprofen, maybe, because it is an anti inflammatory but acetaminophen?  I don't see that it would have any impact on the test results to take Tylenol.