Can implantation bleeding last 6 days?

Doubt it: Sounds more like a menstrual period. A positive pregnancy test can tell a woman that PRIOR spotting was actually implantation spotting. It can be hard to tell if a woman 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 (3 weeks after when conception might have occurred).