Eating sugary foods, caffeine, etc, can cause a lot of the symptoms you're describing. Especially the fact that you said you feel BETTER if you eat something sugary. That is an important signal. Even while you're waiting for the results of your tests, I would take a serious look at your diet and consider cutting out sugar, caffeine (coffee & sodas) for a couple of weeks and also make sure you're getting enough protein and vegetables and other nutrition. Alot of people eat excessive carbs too throughout the day without getting the nutrition they need. You would be amazed at how much what you eat can give you symptoms like these.
My latest example: I was putting a lot of artificial sweetener (Equal, Splenda, etc) in my coffee daily (for a year or two) and I started having vision problems after using it each time. Took a while to figure out what it was, but I found out it was the artificial sweeteners -- I did some research and man they are nasty chemicals in there -- my vision was 100% fine after I stopped. Now I use honey or agave syrup.
Hope you figure it out and feel better soon!