How Long Do Birth Control Pills Take To Cure Hot Flashes?

I am 53 years old, 40 lbs overweight came on due to onset of perimenopause- can't seem to budge the weight, on high blood pressure meds. Walk/powerwalk 25-35 miles a week- on low fat diet. Last week I went on birth control pills to deal with my severe peri-menopausal symptoms (altho my hormone numbers are sometimes in the menopausal zone) while it has helped with the horrible depression/anxiety/crying my hot flashes are terrible.. day and especially night. How long will it take for the birthcontrol pills to deal with my hot flashes?