Me and my girl friend had sex on aug 27th.
On 29th Aug I gave her Unwanted72 (contraceptive pill).
On 10th Sep she got her periods.
But from Sep 10 to till date she didn't got her next period.
Is she pregnant by any chance

Could be !
But still unsure.
Have her take a test.. if it shows positive, she will need to go to a doctor to comfirm it.