BFP but days PG on app don't make sense

Heh. Doctors do the same thing. It is because technically your body has been preparing for the extra while beforehand to produce a baby.. That's what menstruation is! Just usually your body is surprised by not being fertilised and sheds. Therefore your body is preparing for your baby before you even have sex. So the doctor (and the app I guess!) Give you an extra week or two than you would first expect. I hope this helps!

Medical count it a bit different. Not all know when they ovulate, and.. the medical site says women should be pregnant for around 40 weeks, so..'.it is count from the day of your cd1.

Yeah it is quite weird but you weren't even pregnant yet for the first two weeks!

They go by the 1st day of your last period to calculate how far along you are. Even if you know when you ovulated, they go by that. Not actually from the time of ovulation. 

Yes, Mae is right. Because most people have no idea when they ovulated and it's impossible to know when implantation and fertilization took place, the way they count how far you are is by the first day of your last period. I also ovulated on the third this month! My last period was 7/18, so that makes me 4 weeks and 4 days pregnant, even though it's technically only been a little over 2 weeks or so.