Measuring's???

Karlee • ❤️ Soon to be mom to Giovanni Sebastian Francis Fliegel ❤️
Okay so my OBGYN told me at my appointment Monday that my son was measuring a week ahead at my last ultrasound (30-31 weeks) 
I am 33 weeks now.
She said that I am measuring smaller then I should be but he's measuring ahead so she wants to do an ultrasound the 13th to see if he is growing properly.
She also told me he could possibly be earlier then we think... 
Anyone else having issues like this?