I am 28 years old and have had secondary amenorrhea due to anorexia for the last 8 years. I have recently gained weight and although I'm not 0 healthy my body is getting back to normal but I have not yet had my first menstrual cycle. I have also recently got a boyfriend and we have become sexually active. I started tri-sprintec this past Sunday both to bring onmenstruation as well as for protection from pregnancy. I have two questions. First, I'm not sure if the pill will start working immediately or after 7 days since I dont get my period. So should I use back up for the first 7 days? Secondly, I noticed the pack of birth control expired 09/08. I only took sunday and Monday pills and I started a new non-expired pack today. (I took the 3rd pill of the new pack). Are the two pills I already took still effective? Thank you for all your help!