Most probably you are not
pregnant. I-pill is a harmone based drug and it interferes with normal cycle or rhythm of body's own harmones. Even though its over the counter drug, its always better go take any medication after doctor consultation. The brownish discharge indicates bleeding that occured some time back but is coming out of the body later.
Next Steps
Wait for your periods to resume. Repeat a
pregnancy test if periods get delayed by one week
Health Tips
If you and your partner arent planning a pregnancy any time soon, consider opting for a contraceptive pill on regular basis to avoid such distress in future. Prevention is better!