What happened to the 2nd trimester?

I am currently 23 1/2 weeks, still in my 2nd trimester.  But these boys have had a MAJOR growth spurt in the last several weeks.  Last week I when I went to the OB my uterus was measuring 28 weeks!  Which is totally normal when you are having twins.  The babies themselves are most likely measuring much smaller, but we won't know for sure how they are growing until we have an ultrasound in 2 weeks.  I'm definitely looking and feeling like I'm in my 3rd trimester already.  I feel like I went from 2nd trimester to 3rd all in a matter of weeks.  But it is all good because that just means they are both growing!  I feel like they haven't been quite as active in the last week (especially baby B), but maybe that just means they don't have as much room anymore.  Here is my belly at 23 weeks...(my belly button has completely become an outie, btw :))