Hello, I would be happy to help you with your question.
In the setting of unprotected intercourse
and a change or delay in your period, the assumption has to be that you might be pregnant. It is possible that you did the test slightly too early. It should be repeated in one week. If you are not pregnant, then there is something abnormal about your cycles and when or if you ovulated. This should be discussed with your doctor.
I hope that this helps. If you have more questions, please click on "ASK ME A QUESTION" link above to directly ask me a question!