Not hungry

Has anyone reading had a baby that just did not seem to have much of an appetite?? This is Brooke (and it was Ryan, too, but I actually think Brooke is worse from what I can remember of Ryan). She can go 12 hours over night without eating and then get up the next morning and take *maybe 4oz. Then her 2nd bottle of the day, which is usually 3 hours after the first, she is even LESS interested in. Just now I tried feeding her after she drank a measly 4oz. at 8:30 and she took 3oz. and is done. She normally eats every 3 hours during the day and if I'm lucky it totals out to about 25oz. total for the day. Yesterday she only drank 19oz. all day. I've tried going 4 hours between feedings and it does not phase her at all to wait that long and she doesn't drink any more that way or seem any hungrier. Feeding her that way only equals out to 4 feedings a day (like 8am, noon, 4pm, and 8pm) and usually ends up in her drinking less than she would eating every 3 hours. She just does not increase her amount EVER, even if she goes 5 hours between eating. With her slow weight gain in recent months this has me a bit concerned and it makes me uneasy that she just seems so NOT hungry. She can be a real pain to feed most of the time, too. She is VERY easily distracted, even when nothing is going on. And then she'll stop eating and does not care to finish. I just don't know what to do with her! I know I can't make her eat, but I'm worried about her weight gain : (. I hate that I worry so much about this, but I don't know how to NOT worry : (.