It is not normal to be lightheaded this far out from surgery. Your doctor should know about this right away. They will need to know if this is something new or has it been a problem since right after surgery. The causes are very few. They all relate to not getting enough blood to your brain which makes you feel dizzy.
You could be dehydrated and need more fluid. If you are on diuretic medication, it can increase your fluid losses and cause these symptoms. Have you had your blood pressure checked? Have you had your blood count checked? Did you have excessive bleeding during and after surgery?
If you did, you body has not fully created your normal blood level and is not carrying enough oxygen to your body. When you get up to fast or exert yourself, you can feel lightheaded.
Also, what medication are you on? Not uncommonly, you can get this feeling from narcotics, such as Tylenol # or Vicodin. Your doctor should be able to evaluate all these questions and help you to eliminate the problem.
Contact your Plastic Surgeon's office today.