What could be a possible reason for no period while on mini pills but a pregnancy test is negative?

Well I do not know a whole lot about mini pills but I do know that while on regular birth control pills (such as Yaz, or Loesterin 24 Fe) they can cause you to miss a period or be late for quite a while, especially when just starting them. There are several things that can contribute to a negative pregnancy test even if you are pregnant. Some medications can give you a false negative, the timing of the test can affect the results. If you did not follow directions properly; if you let the test sit for too long the results may read negative after a while. It is important to read the results within the amount of time given on the instructions of that particular pregnancy test you bought. If you did not perform the test properly (example: you drank a lot of fluids before taking the test, which can dilute your urine). Etc