I have a Labrador, she is pregnant and vomiting, please help?

I need a favor I have a Labrador, she is pregnant around her 40th day. As it is her first time, our vet suggested that we give her calcium, a dose of 4 ml two times a day. whenever we give her that she vomits after 2 - 3 hours of her dosage, today we tried skipping her calcium dose but still she vomited a bit. Is this vomiting symptom normal in these days of pregnancy or something is wrong. please suggest.