Useless at the nub and skull theories

hello,

i am an expectant mother due on march 13th 2017. I am currently 16 weeks and all my check ups have been spot on but I am desperate to know the sex. I've heard of the theories such as nub, three Dots, skull etc but I'm rubbish at looking. I just wondered if I could have peoples opinions on the gender of my baby by my ultrasound.

Thank you 😊