diabetics

Can the doctors miss diabeties? 
I passed my 2 hour glucose really well... I did walk home then back (I was told to leave and come back) I don't live far from the surgery. I had a normal blood test before this too which I fasted for as well and no bad result. 
I'm having a bad headache I'm always thirsty bad taste in my mouth and I'm having dizziness. I'm 31 weeks! Should I be worried? Or is this really all a coincidence. I had headaches in the first trimester too! I'm so crampy as well I just feel poop!!!