How soon can I have sex without a second back up method after starting a new birth control? I started a different type of birth control last sunday and my normal doctor told me i can start having sex without a back up method in only just a week. After doing some research I have read otherwise, now I want some personal opinions. Im 18 years old and about to start college in the fall, but ive been with the same man for 4 years and were engaged. So pregnancy wouldnt be the end of the world. We actually kind of want a baby we just want to settle into our new home first. I just want to know personal stories or advice. Thank you!