With 3 pregnancy
tests negative and missed periods it is less likely that you could be pregnant ,it is due to the hormonal
changes that you might have misse dyour period,just get a sonography
done to rule out any ovarian cyst
which might have delayed your periods.
regarding the white discharge if it is not symptomatic then nothing to worry,but if it smells bad or leads to itching or any other such symptoms then just see your doctor once to rule out local infection and get appropriate medication.