Post partum sex while breastfeeding..

Jessica • Wife💜; girl mom x2 , and a bonus son 🤍

My doctor cleared me today at my 6 week check up to have sex again. He then told me I “can’t get pregnant within the first 3 months of breastfeeding” , which I thought sounded wrong and definitely don’t want to take ANY chances. Has anyone heard of this ?

He can’t place my IUD until the end of March👎🏼