help?! breastfeeding and pacifier ?

Caterin • Hi I'm pregnant with my second, my first is 4.
First time breastfeeding and my son seems to drink enough milk but then continues sucking as to soothe himself back to sleep but ends up drinking to much and spitting it all back up. I read not to introduce a pacifier until after 3/4 weeks when he has gotten used to my nipple. Anyone introduced a pacifier from the start ? How was it ?