Taking an emergency contraceptive pill like i-Pill commonly delays or disrupts the next period by days to weeks, which is very likely what's causing this. The bleed you had from August 29 to September 1 was probably the withdrawal bleed the pill caused, not a true period, and the brownish spotting now fits with your cycle still resetting.
Next Steps
Since your last
pregnancy test was about a week ago, repeat a home test now to be sure. If your period still hasn't returned in another one to two weeks, see your gynaecologist for a hormone check and pelvic ultrasound.
Health Tips
Go in sooner if the spotting turns into heavy bleeding, or if you get pelvic pain or fever.