Gf has pcos had what looked like implantation bleeding then a milky white liquid a week later is this be pregnancy? Or part of pcos? Test was negative

Unlikely. Home pregnancy tests are very accurate, so it is unlikely she is pregnant. Pcos (polycystic ovarian syndrome) often causes irregular bleeding. White discharge is likely to be the body's response to hormones. If she misses her period this month, she can be evaluated by her doctor.