please could i have some advice.

Ok i had my last period on the 30 oct for 5 days. normally they last 7-10 days. it was late so i tested and it was negative. i have just finished ovulating. now me and my boyfriend have baby danced the whole week i was fertile. for the last 2 days ive felt awful. back is sore slight cramping in my tummy. feeling sick. im not due on for another 12 days or so. is it possible or is it just woshful thinking?