Breastfeeding Affect Conception?

ALB
I breastfeed my 18 month old toddler 5-6 times (on demand) a day. We are ttc#2 for a couple months now and still no baby. Ive had no problems with the first conception.
I came away from my doctor office today with the answer that "breastfeeding can make conception harder." I am heartbroken if this is true. I would like to continue breastfeeding until my toddler weans herself.  I will be heartbroken. But if I want a second baby now at my old age, then I'd better suck it up and try this out. My fear in the end of this is no baby and losing my breastmilk. 
What are your experiences?
I fantasized that I could continue to breastfeed my toddler while being pregnant. My mother who had 10 children said there is no breastmilk to give a toddler during pregnancy. Is there any truth to this? I'm skeptical.