A concern or don't worry

Diana • Wife since 5/25/13 first time mom to the beautiful Olivia Rho

I have a 4.5 month old and for the past week she is wanting eat every 5 hours and then sometimes doesn't take the whole bottle. If she eats the whole bottle it's 6oz if she doesn't I'm lucky she will eat 4 oz. I have started cereal she doesn't get it every day and eats that great! Is this a concern or don't worry?