What Causes White Discharge From Nipple While HPT Is Negative?

i am a 25 year old woman. my partner and i are trying for a baby. about a week ago i had what i thought was my normal period but it wasn't as heavy as it usually is and also only lasted for 2 and a half days on and off (it normally lasts 4-5 days constant flow). i now have a white discharge coming from my nipple when i squeeze my left breast. i took a home pregnancy test today but it was negative. could i still be pregnant? should i go see my doctor. i am worried.