baby refusing to eat.

my baby is 4.5 months old, and for the past few days, is refusing her bottles. she wakes up at 8am, and won't drink more than an ounce or two at a time until around 5pm. at bedtime (10:00pm) she will drink 6 ounces, and sleep until 3 am. at 3 am, she wants 4 ounces, and again at 6am. she used to sleep from 10 to 5am, but now is up all to eat at night several times. any ideas as to why she won't eat during the day? she doesn't act hungry, and even if I offer her a bottle, she plays with it, but won't eat....