Prep for an u/s?

Liz
Ok, when I went in for my first u/s the dr didn't tell me anything. I'd already been waiting for 40 mins past my appt time when the nurse came out and told me to drink water! When I asked how much, she just said lots! 
​I didn't have any with me, so I had to drink from their cooler-the water was ice cold, and downing so much have me a headache, and had me shivering...after all that they still had to switch to a transvaginal u/s!
​So my question is this...I have my 2nd u/s in 2 weeks, they've told me nothing again. What do I need to do to prepare for it?! 
​Thanks ladies!