Can I still be pregnant?

Brittany • Mother of 3 two daughters ages soon to be 8 and 4 and a son soon to be 6 hubby and i are ttc baby #4 to complete our family!!!!
My AF is due Sunday and I tested last night so 4 days before my AF and with a dollar hpt and it was a negative! Could I just be testing too early or am I most likely not pregnant?