Even formula fed babies can wake often, despite the myths that they sleep better (usually not true).
Yep, DD is FF and still wakes at least once a night, sometimes twice a night. Just give it time, at 4 months your little one is still just that, little, and chances are probably needs those feeds. Sleep deprivation is hard, but try and enjoy the nightly snuggles, one day you'll probably miss that time!