Hi!!!!!I ll try my best to clear you confusion Kanchan.Let me take it on one by one.
Monthly bleed can be 3-4 days prior and 3-4 days post to the date of the previous month bleed.So the due date can last for 3 -4 days and as your pregnancy
test has come out negative, you need not be stressed.
Now coming to the discharge part.A brown discharge instead of a period normally happens because of late periods. The body of a woman expels the old uterine lining in this condition. These discharge usually last for three days, and then a female has her usual period.The vaginal canal is a self-cleaning system that expels dead cells and lining. Sometimes, when the uterine lining is not eliminated, it resides within the uterus
for up to a month. This is why women experience brown discharges instead of periods.
So,you should be getting your normal bleed soon.