Suggestions about baby sleep!

My little nugget has been a great sleeper! Sleeping since 6 weeks old! Everyone an then she would wake up in the middle of the night I would get up change her and then feed her and she would pass right back out. She is now almost 8 months and is waking up every night. The doctor told us that as long as she is getting enough food during he day (which she definitely is!) then we should let her cry it out.