I started taking birth control a week ago and it dried up all my milk. Do I have to wait 3 months before getting a reduction?

Dear kersten2,
most plastic surgeons will recommend you to wait at least 3-6 months prior to surgery. But every plastic surgeon has his own preoperative protocol, which he recommends to his patients. I would suggest you to discuss this with your plastic surgeon.
Daniel Barrett, MD

Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

Following breastfeeding, it takes at least 6 months for the breasts to adjust in size and shape. In addition, there is hypervascularity of the early post-pregnant breast which increases operative risk. 
I recommend waiting until the process completely subsides before contemplating surgery. 
Visit a board certified plastic surgeon for in-person evaluation and discussion.
Best wishes...