I got my last periods on 25th April 2013... Since then my husband and I only did oral sex.. also I did a pregnancy test at home on 24th May 2013 which was negative... Am I pregnant or what?? why am I not getting my periods?

First, a pregnancy test at that time is not very accurate. However, if there was no penile insertion since your last period, pregnancy is unlikely.

You didn't say how regular your periods are. But there is no way for us to diagnose the problem. If you are concerned visit your doctor.

You can not get pregnant from oral sex.

But it was just time for the period, when you took the test, so it would be negative.
You may try to test now, using first urine of the morning

But many reasons, infections perhaps, medical issue, but wait and see if you have this months, if not, see your doctor for testing