How Can Vomiting After Taking Birth Control Pills Be Controlled?

Hello, my friend has been vomiting randomly for the past 3-4 hours. She says she gets sick whenever she takes her birth control medicine (to make periods less extreme), so after a few days of being sick, she will cut the pill cold turkey. She has already had the prescription bumped down 2-3 times and the doctor said the dosage is about as low as they can go. Why is the pill doing this to her and is it possible to make it work for her? She's 18 years old.