Breastfeeding while Pregnant

I am about 8 weeks pregnant and I am still nursing my 1 year old. I was told by my Obgyn that it might be best to wean him because it takes a lot of energy and resources to breastfeed, as well as to create a baby. I am wondering if anyone kept breastfeeding through your pregnancy and everything turned out fine? :) Or if anyone has heard of another opinion from a medical professional?