If it is Type 1 Diabetes, you are somehow born with a weak pancreas or abnormal hormone system which causes the lack of insulin production. But about 90% of the diabetes patients are of Type 2 Diabetes which is still remain a myth among the Smart Scientists.
Type 2 Diabetes is a diet & lifestyle related illness. Most people put the blame on the Sugar and Carbohydrate for the elevated glucose level in the blood. Actually, it is not the 'sweetness' of the modern diet that causes Type 2 Diabetes, it is the Acidic by-products that accumulated in the cellular environment that hinder the function on insulin to bring in glucose into the cells for energy production or storage. This condition is commonly known as Insulin Resistance. Type 2 Diabetes is not because of lack of Insulin but the inability of insulin to perform its task to open up the glucose channels into the cells and when the glucose cannot enter the cells, it bounce back into the bloodstream and causes hyperglycemia.
How do you know if you have hyperglycemia? Well, remember the "3 More, 1 Less" symptoms. First you have More Thirst for water, More Hunger for Food, and More frequent toilet visit. And if the condition get worse, you will notice drastic weight loss which will result in Less body mass. When you reach the Less phase, that is when your body cells start to degenerate which will result in the malfunction of vital body organs.
There are other causes of your symptoms and I hope you've mentioned them to your doctor. If you're concerned about your blood glucose levels, you can purchase a glucose monitor pretty cheaply at drug stores. I got one a few years ago for $10 at CVS. They usually come with 10 test strips and 10 lancets and instructions, which should be plenty to check your blood sugar throughout a couple of days. Extra test strips can be pricy.
If you go this route, most recommend checking your blood sugar first thing in the morning (fasting) and 2 hours after meals. Some people will eat a high carb meal (about 70g of carbs) and check their level at 1 hour, 2 hours, and 3 hours after you've eaten, which is similar to the glucose tolerance test given in a lab to check for diabetes. If you do this sort of test, you may want to fast 8-12 hours before your "carb load." The ADA guidelines say fasting glucose over 130 and 2 hour post meal levels over 180 suggest diabetes. Lots of things can influence your blood sugar including exercise, stress/lack of sleep, and overeating. There are a few guides online that can walk you through the process of self testing for diabetes. Hope this helps and hope you find out whats going on! Good luck.
"Over the past few years I've had several blood tests done to see if I'm diabetic and each one comes back negative."
Have you considered an allergic reaction to refined sugar? Why don't you eliminate sugary foods/liquids from your diet and see what happens. You should know in a week. If you need to sweeten something use Splenda, a sugar substitute.
Foods to avoid: No canned or packaged fruit, packaged pudding [ALL deserts], ice cream, snacks cakes & pies, muffins, healthy sounding cookies and energy bars, bottled sauces [spaghetti & BBQ], dairy products like milk. When you look at food ingredient labels sugar is listed in 'grams'. Quite misleading. Every 7 grams equals one HEAPING Tablespoon of refined sugar.
Post back and let us know how you're doing.