I have this very same issue my friend. Look at my post today entitled "Anxiety at best, something terrible at worst."
I have been fighting this demon for two years now. Does it happen after you eat? Do you feel better in the evening/night?
From my experience if you only get dizzy when standing up or changing positions you might want to check out Dysautonomia International site. Look into (POTS) Postural orthostatic tachycardia syndrome. If your heart rate goes up when you stand up and the place is spinning might be something to look into.
I can't believe that no lab/blood work has been done on you? That is typically the first things done...at any rate...do you drink enough water throughout the day? Being that our body's water percent is around 65%, if you are lacking (aka dehydrated) you can have those symptoms. Try increasing your water intake and see if that improves your symptoms. The next thing...look on your browser for Cawthorne's Head exercises and give them a try as well. Sometimes we get crystals in our semicircular canals and that can cause dizziness..with the exercises, you can relocate them, so it doesn't put your equilibrium out of whack! Good Luck!