Plan B not effective at all for women over 176 pounds?

Hi all! I just came across this warning on Plan B website, and I am over 250 pounds. Wondering if that means Plan B with me is not effective at all?
I took it before ovulation, but then had unprotected sex all throughout my ovulation period. 
I now have extremely sore breasts and spotting for the past 3 days. Period should start on the 17th. 
Could I be pregnant?
Thank you! :)