Hi & Welcome.
I can understand your problem regarding the efficacy of I-Pill.
The chances of
pregnancy are low.
As per the WHO (World Health Organization) the post coital
contraceptive pills like I-Pill is 85% effective in preventing unwanted pregnancy even it is taken within 2 hours of an unprotected sexual act.
In general these drugs claimed to effective for 72 hours. But as the time passes chances of failure of drug increases progressively. Since you had second unprotected sex within 24 hours of the first one the pills and wait for withdrawal bleeding.
You may have a normal period within the next month as your next period is expected on September 25th,2016 or sometimes, the I-Pill can change the length of your monthly menstrual cycle, making your next period come as much as a week earlier or a week later than usual.
If your next period is late, you may consider getting a home pregnancy test.
Remember, try to avoid I-Pills use frequently in future, as it may lead on to
hormonal imbalance and menstrual irregularities so, keep these drugs reserved only for emergency situations.
Hope this will help.