i had that too.. couldnt sleep during the second trimester.. sometimes, i'd wake up at 2am, 3am and be wide awake like it's 10am!
unfortulately, i havent had a good night's sleep since my 2nd trimester.. and that's been almost 2 years!
it's your body's way of preparing you for sleepless nights, tho i think it should just let you enjoy the last few weeks of blissful sleep.
I'm waiting for another 5, 6 years till i can sleep thru the night again..