Vomiting after stims

Started my ivf STIMS on the 21st.. so it's been about 3 days. Last night after my gonal and menopur shot I got really nauseous. I decided to lay down and take it easy, but I ended up getting sick immediate ...twice. I've read this is a common side effect of overstimulation, but I don't think I've been on stims long enough to be overstimulated. Any thoughts or similar reactions?