My period is late, negative PT?

So I am on the pill and I was suppose to start my period saturday. Now usually on the pill I don't start until 2 or 3 days later from the time im suppose to start. Well My period never came after 2 days so I took a pregnancy test and it was negative. I took another one the next morning, 4 days after the time I was suppose to start my period and still the test was negative. It will be a week tomorrow with no period and I am very worried. I started taking GNC Women's Ultra Mega Active supplements about 2 weeks ago, could this be effecting my period? With my daughter, my test showed I was pregnant very early on.