15 dpo, no AF

I never got a fully pos opk so I'm going with my darkest line. With that I'm 14-15 dpo and AF was due today. I've had cramping on and off, even to the point it felt like I had a tight band around my lower abdomen (weird feeling). I also had cramping when doing Turbofire (cardio ab workout) and had to stop (never happened before). My wondfro test was a bfn today. Wondering if I could still be pregnant. I've been trying for a year.