i am going through the same thing, i was suppost 2 be on my period about 2 nearly 3 weeks now, ive got worries about, ive took 2 pregnancy tests and both turned out negative if your period doesn't come on in the next week, take another pregnancy test and if its still negative then make an appointment with the nearest hospital to get a scan. that what i'm going to do.
Have you had any sort of sickness bug? =D
hope i have helped x