how far along?

Noleen • Married summer 2015
Hi, without sounding stupid how do you know how many weeks you are? I know they add two weeks on from date of conception, however my cycles were shorter, 23 days and I ovulated on CD 9 with an LH of 14 days. I ovulated exactly 4 weeks ago today and I know most people would add 14 days, do I only add 9? I'm so confused lol