So I usually breastfeed my son but once in a while he'll get a bottle like when I leave him with my…

So I usually breastfeed my son but once in a while he'll get a bottle like when I leave him with my mil. So today I latched him on and he ate for a while and was good then he started crying and he was rooting so I figured he was hungry however he wouldn't latch on. Finally I gave him a bottle and he drank 4 oz. anyone know why he might not have wanted to latch on? I love breastfeeding him and it broke my heart