When does the 2nd trimester actually start?

Smilie • Hello our first baby girl is on the way on the 22nd November 2015... Please be a sticky baby 👼 ✨BD to all
Hello :) am 13 weeks today and due 22nd November. Been told different dates for starting your 2nd trimester like 14 weeks 13 weeks and 1 day and 13 weeks and 3 days. 
Just so excited to get into this wonderful trimester. This is our 3 pregnancy 1st loss angel boy 13 weeks and the 2nd was 5/6 weeks. So super nervous and dying to get into the 2nd part and relax a bit. 
Any tips or advice ladies ❤️💙