When does the second trimester begin? I'll be 13 Weeks tomorrow.

My doctor told me 14 weeks starts the second trimester and 28 starts the third
Either way, in excited to be there or almost there lol @happyamy
At least that's what I have been told. But I just looked it up online And it's telling me that the second trimester begins in the 13th week.
@nelly1991, so tomorrow?!. (:
Should I start telling family the news then?