According to your description, is not clear if you are really trying to conceive or you think that pregnancy might happen accidentally (a condom break, ejaculation inside the vagina, etc.). Chances for conceiving are biggest when you have unprotected sex with internal ejaculation during the fertile days of your menstrual cycle. The fertile days are those around ovulation (2 days before and after). Ovulation occurs about 14 days before the next period is due to arrive. Women that use hormonal contraception might have some problems with conception because hormonal contraception (especially depo) has a prolonged effect. Hormones continue to alter the body and influences the chemical balance for up to 24 months after a woman stops taking birth control. 24 months is considered the maximum period for re-establishing full fertility. We can consider sterility only if you are trying to conceive (which means having unprotected sex with internal ejaculation during the fertile days of your cycle) for more than a year without success.