Pregnancy is counted 40wks from the first day of your last period. If you are due July 16th, then your LMP should have started October 10th. So if you have/had a normal 28 day cycle and had a perfect conception (which is almost impossible) you conceived October 24. But because it isn't perfect, give or take a few days of when the sperm reached the egg. I think you are pretty much on schedule. Some people are off 2-3wks of their last period, so you're fine.