if you took the emergency contraceptive as prescribed you are unlikely to be pregnant and the hormones in it will alter your cycle. I recommend taking a pregnancy test in 2 weeks time and again in a further 2 weeks. As Steph has said, you need to consider some method of preventing pregnancies ie birthcontrol of some sort. The emergency contraceptive pill will also not prevent you from contracting sexually transmitted infections.
If you took emergency contraceptive within one hour of having unprotected sex, it is highly unlikely that you are pregnant. The pill has likely messed with your period b/c of the hormones in it. If you still do not get your period in a couple weeks, take a preg test but i really do doubt that you are pregnant.
If you are going to keep having sex, I suggest going on some type of birth control.