Leaking fluid during pregnancy?

Gabriela • First time mom. 23. Due 06.26.17
I am currently 19 weeks and for some time now I have been leaking fluid from down there, and am not sure if it's just vaginal discharge or perhaps amniotic fluid. I did go to the doctor last week, and he checked my cervix and said it was close and also sent me to have a sonogram to make sure my cervix is completely closed.
My question is, would that have showed up on the sonogram or while he was checking me, if it were amniotic fluid? Or is there a special test for that. I'm just very worried. ☹️