So you're just short of 15wks pregnant, right?
I went to an online pregnancy calculator thing.
Not the most reliable.
But by the due date you gave, you should be about 15wks.
Which meanss, on an average 28 day cycle,
you should've conceived at the end of may.
The only way to be 100% sure is to do a dna test
after your baby is born.
How many days is your cycle, do you know?