Newborn going more than 5 hrs

My baby is a week old and in the past 24 hours has seemingly lost interest in eating.  She was eating every 2-3 hours. Her pediatrician recommended not allowing her to go more than 5 hours without eating, but said it was fine for her to go a full 5 hours once a day. Twice I've had to wake her to feed after 5 hours and it took a bit of coaxing. The rest of the day she was eating in 3-4 hour intervals and was irritable. Not sure if she's just having a weird day or if I should call her dr tomorrow. Anyone else experience anything like this!