I think your suspicions about some food sensitivities that you're already noticing are correct. Listen to your body. The blood test for Celiac/gluten intolerance is less than accurate, so if you have a doctor that wishes to rely on this test solely to confirm gluten issues--get a different doctor. No one should be that stubborn about what is happening to you and your own body and doctors need to listen to their patients better than that.
The food diary may not be sufficient. It would be better to keep track of it yourself on paper, so you can write everything you need to write. You need to write down every ingredient you consume. If it's a meat loaf, for example, you need to write down what is in that recipe or it won't make sense.
If MSG is suspected, you should look up Tyramine Intolerance and avoid the foods on that list. The usual signs of MSG intolerance and Tyramine Intolerance are IBS and migraines, but that doesn't mean there aren't more outward visible signs on the skin involved with such an intolerance. You should also avoid food preservatives, such as sulfites, in general. This means avoiding pre packaged and prepared convenience foods.
A whole foods diet simplifies following an elimination diet and truly helps you know and understand what you are eating and drinking.
This does sound more like a food sensitivity/intolerance rather than what is considered to be a "true" allergy. You are less likely to test positive for actual allergy with the tests a conventional allergist does with food sensitivities and intolerances. A good allergist will recognize this as fact and will respect the fact that you know your own body and how you react to certain types of foods even if their tests come back as negative for such allergies. I like my allergist because he used the example of an anonymous patient who will test negative for milk allergy but could drink a glass of milk right there in front of him and still have a reaction to it. This is a reasonable response from an allergist.
The best way to identify food sensitivities/intolerances, then, is to see a naturopath and follow instructions for an elimination diet. It's a long process. And, while you will never get results that a conventional stickler of a doctor will accept as fact since some only accept the results of their skin and blood tests, you will know for yourself which foods bother you the most. You will have to ignore the nay sayer type of doctor who won't accept the results of an elimination diet if conventional allergy tests are all negative. It's your body and you know what happens to you better than they do. There is an ER doctor at the local hospital who is one of these sticklers. It seems like she is one of those people who assumes that gluten free and casein free diets are some kind of popular fad diet. I ignore her. I will have friends bring food for me if I'm in the hospital again if this is how the local hospital wants to act. When one is feeling lousy enough to be in the hospital, it's not like one is going to feel like eating a lot of food, so I don't see why this should be considered unreasonable. The hospital may see this as unreasonable, but I know what happens to me if I eat gluten and dairy for very long or foods on the Tyramine Intolerance list.
Try looking up information online about eczema. I don't know if cracked corners of the mouth can be called eczema, but the reaction is still there to the gluten and dairy. I think you will still benefit from the information.
Here's a link to MedHelp's Food Diary
Keep us posted. Maybe this diary can help you!
I just re-discovered a great link that can help that concerns sulfites: