I just bought my prescription for tri-sprintec birth control and i was wondering when it is safest to have sex without a condom. i am 18

If : If you start the tri-sprintec during the first 5 days of your period, you are protected against pregnancy immediately. If you start any other time during your cycle, you need to use a back-up method of protection like a condom for the first 7 days you are on the pill. Of course, it's important to remember that the pill protects against pregnancy, but not against sexually transmitted diseases (std's). Only the condom helps to protect against std's. Good luck!