Gf took two pregnancy test both were faint but positive took another a day later and it was negative could she be pregnant?

Maybe not pregnant: Can retest after 7 more days. If test results had changed from positive to negative, a woman might have been briefly pregnant and naturally miscarried. A urine pregnancy test, done correctly, gives a very reliable result 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period. If a woman gets her normal regular period, then she is not pregnant.