Is it possible to throw-up while taking Zofran?

I know it's an antiemetic, but I'm still curious. I have Gastroduodenal Crohn's Disease, as well as acid reflux, and with a flare I constantly feel ill. My doctor prescribed me 8mg of Zofran every 6-8 hours as needed for nausea. However, even when I take it I sometimes feel nauseous. I didn't know if that's caused by anxiety, or whether I really am feeling sick. I know phenergan makes it physically impossible for you to vomit while taking it, and I had that before; but my doctor felt that Zofran wouldn't make me as drowsy (and it is much, much cheaper). Also, I read that if you take a Benadryl with the dose it may work better, is this true? Any answerer experience or tips would be great.