Vomiting is unfortunately common with the prep, and despite it, the bowel is typically cleaned enough for an adequate exam. Often, nausea will subside if you slow down your intake of the prep solution and/or the water, by using a straw and chilling the liquid. Take a break and wait 15-30 minutes, then try again at a slower rate. For the second prep dose, at least double the time to ingest the prep.