I co sleep and breastfeed my baby. When he wakes up at night he's always just latched on to my boob…

I co sleep and breastfeed my baby. When he wakes up at night he's always just latched on to my boob while half asleep ate a little and then went right back to sleep... Just recently in the past couple days when he wakes up at night he won't latch on and he just tosses and turns and eventually will start crying and the only way for me to get him back to sleep is to rock him or bounce him.. Is this just a phase? What could be wrong? Could it be cause he's teething?