3 week old only sleeps with a bottle?

My baby sleeps all the time. When she does wake up it's because she's hungry or needing a diaper change. After I feed her and change her she usually won't go back to sleep until i give her more formula which she will only drink maybe a half ounce and then falls asleep. She acts hungry but always falls asleep before eating much. I thought it was just because she wants something to suck on but she won't take a pacifier. By giving her this extra milk after she is full, I'm not overfeeding her am I?