Can my employer require a physician's statement stating the reason for absence?

I have had to use more sick leave more than usual since August 2011 (14 sick days, 9 vacation days).
Family issues with a family member's drug use, my daughter's separation from her husband in which she had to move in with us with her two grandchildren, as well as, my husband's chemical plant being on strike for 7 months has caused alot of stress & has obviously lower my immune system. I had leave hours to cover all my leave taken, the leave was approved by the employer & I worked weekends & worked overtime to keep up with my work (with no additional pay). Now my employer has given me a memo stating that I have to provide them with a statement from me stating the details of my illness even for 1 day missed. I also have to have a doctor's statement stating the reason for my illness after 2 days missed. I have to submit a statement from the doctor stating my present is needed if I am caring for a family member. I also have to follow a different procedure for requesting vacation leave than all the other employees. I don't think the details of my illness is the business of my employer & see these requirements as harassment & would appreciate any advice you may be able to give me.