OMG! I have the same thing happening. DD scared me the first time she slept for 8 hours one night. My doctor said try to feed her every three hours too. My grandma is a nurse and raised 6 kids. She told me that she will let me know when shes hungry. And if she is gaining weight then there isn't a problem. So far everything is fine.
i didnt get dd on a schedule until she was 3 months... and i didnt even really do it. she just fell into out pattern. its all about consistency with babies. as long as we went to bed and woke up at the same times everyday she just started doing it too. i found when we would stay up later or wake up earlier she would get thrown off