From what I gather do you mean that you took the test on Monday, 2 days before your period
was due? Or
was the Monday 5 days after it was due? If it was the first, then you could have just tested too early. Did you use first morning urine?
Could just be that you are having pms or even coming down with something. And there are many other reasons as to why your period could be late...stress, changes in weight/diet, hormonal imbalance etc.