Hello and thanks for your query. I shall make an effort to provide you with good professional recommendations specific to your questions. As your pregnancy test have come to be negative, it is less likely to be pregnant. It may be just your anxiety. This kits are highly accurate. But still I would suggest you to see gynaecologist, for evaluation as you have mentioned that your period is late by month. It needs to be evaluated. So see doctor. With transvaginal ultrasonography, the diagnosis of pregnancy can be made earlier by 4-5 weeks gestation. Irregularities in menses are common, as you have mentioned you didn t had and sexual intercourse, you are highly unlikely to be pregnant. Yet again, I duly appreciate your query to me, I do hope that you have found something useful to help you and I shall be glad to answer any further apprehensions. Sincerely,