Thanks for query,
As you have a negative pregnancy
test done by your doctor there is no chance of miscarriage
It is a early bleeding .Due to hormonal
imbalance the period of cycle disturbed & you may get early bleeding.
Hormonal imbalance may occur due to tension,Anxiety,Late night working hours,shift duty,Ovarian disease
It may resulted in prolonged spotting also .
so nothing to worry it may be regular in 2=3 cycles.if you have more than that irregular cycle you may contact your Gynecologist.