Could I be pregnant?

I took two blue dye tests around 3 weeks ago, during when I was supposed to have my period, and negative. I then took two more a week after my period was supposed to be and negative again. Could they be wrong? I know blue dye can be false but they had no signs of positive. I am supposed to get my period a week from today and I gained a little weight and i’m nervous that I could still be pregnant.