Conception

[mentality]

If you are 3 weeks pregnant how many weeks ago are you likely to have conceived...would it be one?

The number of weeks are counted from the first day of your last period. So if your period was 3 weeks ago then you would be classed as 3 weeks but only actually conceived about a week ago which wouldn't show on a test yet.

Is this based on a digital test? They're not awfully accurate, but they work from conception, not LMP which is more normal.