I have a 6mos old baby & last month, i had a brown discharge a week after my period. now today, according to my period tracker, i'm already 4days late?

Test: In the weeks and months following delivery, the menstrual cycle can be irregular. Especially if a woman is breast-feeding. If you think you could be pregnant take a home pregnancy test. If you don't want to be pregnant make sure you're using adequate birth-control. Otherwise some irregularity in the first year after birth is normal for one's menstrual cycle.