Figuring out number of weeks pregnant

I found out 5 days ago that were pregnant. The doctor booked me in for a dating scan for 3 weeks time but im trying to get my head around how many weeks pregnant I am now. The doctor gave me an estimated due date of 17th June 2018 & so did another app however 2 other apps said 24th June 2018.

I have a 35 day cycle & I know I ovulated 2 weeks ago so how is it calculated?

I have read multiple things, one said it's calculated from the date of your last period (which would put me at 5wks) & another said it's from when you ovulate then add 2 weeks (which would be 4wks).

That one week is confusing me! Hoping someone can shed light on this for me. Thanks ladies