Thank you so much guys! This helped a lot.
RockRose explained really well and I don't want to repeat her, so here is some other info. The system to say how far along you are is based before we medically understood quite as much. So all they used to be able to go by is your last period. Well, its extremely rare to get pregnant on your period, so you get a couple extra weeks added in there. That's why pregnancy is 9 1/2 months....not really 9. Are you still in high school? You could talk to a health teacher to explain it to him. Otherwise if you can get him to go with you to the doctors office, they can explain it.
Ashlynn, everyone gets confused by the way they count a pregnancy.
If you are 7 weeks pregnant, that means you conceived 5 weeks ago, so yes, you conceived around Nov. 13. They start counting a pregnancy from the first day of your last regular menstrual cycle, so by the time you miss your first period, you are officially 4 weeks pregnant, not just the two weeks since you actually DID get pregnant.