Keep getting negative results


So my last period was August 10-14. My period are very regular. AF is suppose to come tomorrow but I have pms signs (normally I’ll start feeling the cramps and back pains a couple days before AF). Two weeks after my period started I had a very light color blood on the tissues but only when I went to the bathroom. Lasted only a day or two. I took three pregnancy test the weekend and one yesterday. They all came back negative. Could I be pregnant and it just be too early or do you think it’s nothing?