Small dark brown blood spotting on day of expected period, and on and off for three days with pms. period or implantation bleeding ?

A person can't tell: Wait a few days. A positive pregnancy test can tell a woman that PRIOR spotting was actually implantation spotting. It can be hard to tell if she is pregnant because some of the symptoms seen in early pregnancy can also happen in non-pregnant women. A urine pregnancy test gives a reliable result about 3 weeks after sex, 1 week after missing a period, or 1 week after having a "weird" period.