Have you checked your blood pressure lately? It may be running low, which might cause dizziness.
Also, if you are dehydrated, you can get these symptoms. With the hot weather we've been having, it surprises me that more people aren't a little on the dry side. Make sure you are getting at least 3 liters of water a day. More if you tolerate it.
As far as the upper back aches, are you at the computer a lot? The height of your chair may not be right for you.
Hope that helps,
Kerry