Has anyone had a negative on lets say 10/11 days after sex and then a positive a few days later? I have no idea when I ovulated or when my period is do (I am 8 months pp,breast feeding and have PCOS)

But I swear I am pregnant. I'm nauseous after I eat, I've had cramping on and off, I'm getting stuffy, peeing more often & my back hurrrtsss. But I got a negative today, is it just too early to get a positive? Anyone get a positive a few days later with a negative on day 10 or 11?