The morning-after pill has, I think, an 80-90 percent chance of working. Also, normally, you would get your period 2-3 weeks after taking it, but since it's nothing but a huge dose of birth control, its effects are probably different for all women, just as is birth control.
You took it very early, which is good - it could be stress or the pill messing up your cycle. However, if you're very worried, you can see if there are any walk-in clinics in your area and get a blood test done.