confusion about 12 or 13 weeks equals second trimester

So today at my appointment I asked my doctor is 12 weeks or 13 weeks starts your 2nd trimester and he said 13 weeks because technically for first two weeks of your pregnancy your not technically not pregnant. So I will be 12 weeks on Monday thinking hey I'm starting my secound trimester and was super excited to announce but I guess I will have to wait till 13 weeks to announce. I guess it will be a valentine announcement lol..