I started getting a brownish discharge today & its not heavy like a normal period but it comes and goes lightly & my period is irregular why is that?

Many reasons for thi: Irregular periods can often be accompanied by irregular bleeding. Your age is very important here. You should have your hormone levels checked, have an ultrasound performed or even a biopsy of the lining of the uterus.

Many causes: You should consider pelvic ultrasound and possibly blood work in addition to pelvic exam with your doctor.