Could be or you could not be. All types of things (stress included) can cause your period to be late. Although some tests say they can tell up to 4 days before your missed period it all depends on your body and what your HCG count is at. You could be 5 weeks and still show only a result of 10 and most tests wont pick up anything smaller than a 25. I'd wait a week and retest if you don't get your period and if you are still showing negative and no period go to the doctors and request a blood test.
if your 5 days late for your period tests should be coming up positive, most home tests show positives upto 4 day BEFORE your missed period if u are pregnant
Your boyfriends mom is right. Home tests do not work until maybe 5 days before you are due for your period. Even then there is a 50% chance of inaccuracy because it's simply too early. You should test on the on the 10th if you know your cycle is longer than 28 days you should wait a few days (they work best on or after you are due). Also, those tests are expensive so you should follow the instructions on the box so you don't have to keep buying them =)