Zofran

I have been taking it for 4 weeks and now I'm so freaked out. My doctor didn't prescribe it to me it was a doctor I had to see wen nine was not there anyway I told my doctor about it and she quickly gave me this look and said I don't want you taking it to much. Zofran was helping me out a lot but now I'm concerned I just also saw it in a commercial about birth defects someone please help what should I do in really scared!!