Breastfeeding & Formula

Shakeya
Being that my milk came in on day 6 my LO pediatrician prescribed him on supplementation milk..... now being that my milk is in, I try breastfeeding first & if it's not enough I give my LO the formula. My LO is spitting up after every feeding & it's scary to leave him alone or lay him down alone. Any other ladies dealing with this? Any suggestions?