Not true. The midwives and obs at the practice I go to are very supportive of bf while pg. My mw even started to suggest tandem until she remembered my v. low supply issues.
However, word of caution, it is not easy on the body, nor is being pregnant with a young toddler even if you are not bfing. If you are young, fit and in good shape and it is really what you want it is perfectly doable though. Pregnancy is a doddle for some women and very hard on others. A good support network (someone to give you a break from dealing with a toddler after you have spent the entire day throwing up or to cook for you etc) will really make a difference.
But again, your dr is talking BS