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.
I took the test 2 days before it was due with the early detect. I took it because my husband and i had unprotected sex and i alway like to know ASAP and cant wait. but it came back negative. I also took it because i had no symptoms of my period coming like i usually do. other than sore breasts. a week and a half before that i was getting headaches and light headedness. My period came a day later but not as a period but dark brown spotting only when i wiped. Its 3 days past and the spotting has somewhat ended and there is still no sign of my period. my period is regular. my last one was one feb 16th. This past week i could fall asleep at my desk if i allowed it. I have not changed my diet and I am not sure about the hormaonal imbalance because i went for my yearly check up in January with blood work and all and nothing came back irregular. My weight has stayed the same for the past year however i have put on 2 pounds in the last 2 weeks, but i have not changed my diet. I eat my regular spinach salad for lunch, pear for breakfast and normal suppers. I used evening urine as the early detect pregnancy test says on the box that you dont have to use morning stream.
I would just test again to be sure...you should ALWAYS use first morning urine, I find it strange the box would say this. First morning urine is the most concentrated because during the day you are drinking fluids which dilute any hormones which will be in you urine. If it's negative and still no period, see you doctor.