I had sex the day i took my first pill of my second pack of birth control pill and i was a week late to take it. is it safe? but it was withdrawal

Could be pregnant: If you started your second pack of pills a week after you should have, it's possible you were already close to ovulation. And withdrawal is not an adequate method of birth control: some sperm can still be present before withdrawal. If remembering to take your pills is a problem, you might consider another method of birth control.