I used to get intermittantly v nauseated when I first started taking opioids actually, seemed pretty random and didn't last for more than my first 10 or 20 times.. so it could be that. But it could be many things. See how you go next time, being careful not to mix it with anything and don't take it on a completely empty (or completely full!) stomach (both can cause nausea - full stomach is much worse for me, empty works perfectly, but people vary with this)
Antihistamines can help nausea but if you continue to throw up when you take it in the future then something's not right - too high a dose, bad combination, stomach too empty/full etc..