1. since your menstrual cycle are/were normal, thus this pinkish brownish stuff may be implantation
bleeding [unprotected sex??] which occur between 10-14 days after ovulation and indicates that the fertilized embryo is pushing into the uterine tissue,and occurs around women's expected period, [much lighter and doesn't last as long as a normal menstrual flow].
2. if you are not sexually active, and if pregnancy
test comes negative, could be anovulatory cycle
,so ask your doctor if you suspect this has happened.
3. if taking birth control pills, probably there is breakthrough bleeding
. Make a doctor's appointment to discuss this situation in order to get proper diagnosis and treatment.