What Causes Delayed Period While UPT Is Negative?

the menstruate is late from 26/3/2011 and i made a pregnancy test on 1/4/2011 the result was negative i take a lutofolone on 6/4/2011 and there is no menstruate till now, what i should do ?
I am 25 years old
married from one year and 2 months
I never get pregnant
I am a 73 kg weight and 169 mt tall
My menstruate is regular every 28 days and stay 3 days
My husband has a problem with the count of the sperm
Now i want to if this late in menstruate is normal ( 15 days ) and after how many day should the menstruate from taking the lutofolone ?