should i worry

so its 130pm and just spoke to my partner and asked him what time he got up with little man during the night and he told me 130am (so 12 hours ago) roughly but he didnt take the whole 8 ounces of milk ...well when he woke up this morning i fed him around 8am ish and he once again didnt take the whole lot and fell asleep so when he woke up about 2 hours after i tried giving him the rest but still played up with taking it and left an ounce of milk and he been asleep ever since ...so he has taken hardly anything in 12 hours he normally takes all of his milk and goes about 4 hours between each feed but sleeps through the night (11pm- 7am) he only wakes during night if he didnt have a full feed (which he didnt last night before bed)