Not true at all. People believed this way back because it can cause your period, the actual bleeding itself, to be delayed for longer. But people then realized you can ovulate before you actually have a period/start to bleed. So you very much can get pregnant while breastfeeding. You should never rely on it as a form of contraception. :)

I got prego with liam while breastfeeding macy

..

You can always get pregnant when you have sex. I think they should come up with some super amazing 100% bc, haha. :)