So I had my period on 12.12.2017 for the full length I should. I have then just had my period on 13.01.2018 which again was the full period. The other day I had bad pain in my back and was unsure what it was, I did I pregnancy test and it was postive. I couldn't believe it so I did 6 more. I did a clear blue test which says I am 1-2 weeks but surly i would go by December's period? Meaning im 6 weeks pregnant! Can someone help work this out?