Girls those have had pregnancy or have info about it  -- PLEASE HELP!? I am not going in detail about whom I am talking, Please be kind and allow me to ask the question.

* A Girl has regular period cycle of approx 27-28 days, And she had periods on 10th or 11th of sept.

* She had unprotected intercourse on 20th sept

* She 'thought' she has conceived, but she had 4-5 days long periods (or periods like) bleeding on 4th or 5th oct.

Now, Problem is that she is not having November's periods yet, which should arrive in first week of novenmber, this made her think again that she is pregnant.

She tried 3 diffrent (one tube type and 2 digital) home pregnancy tests within the last 10-12 days, but all the tests are surely negative.

Moreover, she have not had any signs/symptoms of pregnancy like breast tenderness, nausea, morning sickness etc. from date of intercourse to the date.

Summarized question: What are the causes of the missed periods except for the pregnancy?