Your post concerns me. Mifepristone is not a hormone like birth control pills or Plan B. It should only be used on prescription and with a doctor's supervision. Most women who take it are not eager to do it again. It induces abortion or a miscarriage.
In the genral case, the flow would have been heavier, not lighter, and with horrendous cramping. It should induce cramping and bleeding within three days of taking it. Are you sure you took mifepristone?
If, instead, you took Plan B, then a period at the normal time is more likely with lower side-effects and the bleeding, however light, would indicate you are not pregnant.
You also need a basic education in sex and contraception. Teen women are notoriously irregular with their periods. That means that ovulation is also erratic. Any time you have a penis in your vagina you are at risk for pregnancy - whether or not he ejaculates. You are correct only insofar as our fertility usually varies with the cycle but it is a terrible way to plan or prevent pregnancy. Read all the stickies in Women's Health and learn a bit about your body.
If you figure out what you actually took, perhaps we can give you better guidance but what you describe makes no sense from a medical standpoint.
Brandye
Posted: 29 Sep 20:32