Thanks for the query.
While being on contraceptive
pills, you will get only withdrawal bleeding instead of regular menstrual bleeding.
And because of the low level of hormones present in the pills, usually the withdrawal bleeding will be lighter than the normal menstrual flow.
And some women may have complete amenorrhea
for few months.
So no need to worry about it.
If you use the tablets as per the recommend schedule, the possibility of pregnancy
is very less.
The brown tissue you have seen could be endometrial lining which might have shed during the withdrawal bleeding.