Thanks for the query.
Fluctuations in the menstrual cycles can occur due to many causes.
The brown discharge you got on your expected date of periods might be menstrual flow only.
Collected blood in the endometrium sometimes comes out as brownish discharge and no need to worry about it.
Scanty flow can be due to causes like
imbalance due to stress
and strain, dietary changes, poly cystic ovary disease etc.
hormonal abnormalities etc.
So as there is no possibility of pregnancy
, you observe the next cycle.
If same problem repeats, better to consult gynecologist once and get evaluated.