I am 3 days late from my period, tested last wednesday which was a day before my period was due and got what seemed to me to be a very faint line. I tried the test as got really nauseasious and was worried. Since then the nausea hasn't gone away and I've got lower back pain as well, today I'm on my 3rd day of missed period and i tested again and still got what seemed to me to be a very faint line. I've tested both times with amazon bought 'pro matis' tests, should i try again with a different brand? Or is it a definite sign we are not pregnant.