How much liquid for second u/s?

Brittany
I'm 20 weeks today and the paperwork they sent me from the hospital is generic for anyone getting an ultrasound but is it really that hard for them to see baby the second time? I just feel like 32 oz. is just too much my stomach is upset today and I'm trying but it keeps making me sick. I switched to a large glass of lemonade would two large glasses this size be enough?