What is considered 2nd trimester depends on where you look. Many places say its at the end of your 11th week. Some places say the end of your 12th, and others say the end of your 13th. Just a matter of opinion. 11-13 weeks is normally the timeframe you have your 1st trimester check up or when they do 1st trimester screens though since its "towards the end".
Good luck with everything!!!