Is it true that it takes two weeks before your next period to be fertile?

Not exactly: Ovulation is estimated to be 2 weeks before the first day of the next menstrual period. If 28-day cycles, it would mean it takes 2 weeks to go from the first day of the last menstrual period (called the LMP) to get to ovulation day. If 21-day cycles, it would take 1 week to get to ovulation day. If trying for a baby, one should have sex from 4 days before ovulation, through 1 day after ovulation.