Lose Balance and Head Sensations

I am a 72 year old woman. About 15 years ago I began having balance problems while standing. I would lose my balance and have to shuffle my "right" foot to regain my balance. This only occurred 2-3 times a year for awhile and gradually quit happening. It started up again about Jan. 2007 when I was diagnosed with osteoporosis. Now it can happen while standing or walking and it only last seconds and I have it about 12 times a month. I have fallen but not usually so I am concerned about breaking a hip.  I have lost 2-1/2 inches in height. My doctor says each episode is a mini-stroke.

About Nov. 2007 I began having sensations in my head. It is basically on the lower right back side of my head. Sometimes it works its way forward, then to the left front, the left back and down the left back side of my neck. Then it begins all over again.  I have had many blood tests, doppplers, MRI's, cat scans, EEG, echocardiogram w/bubble, cerebral angiogram, etc.  For this I take a baby aspirin, Aggrenox and Crestor.  I would appreciate any advice. Thanks.