how long should a 2 week old sleep

How long should a 2 week old sleep during the night? 
My 2 week old doesn't like to be put down during the day ( crazy I know) but she will just scream until someone holds her, but overnight I was getting about 4/5 hours out of her and the pediatrician said that's great (even though she is still dropping weight she said don't wake a sleeping baby at night, during the day wake her every 2/3 hours) but the past two nights she slept for 7 hours straight.. two nights ago she slept in my arms, last night in the rock and play (first time she slept more than 1/2 hours in there) 
She is my 3rd child but first once I'm successfully breastfeeding, I also have a 10 yo and 1 1/2 yo. My 10 yo never dropped weight after the hospital and that was only 2oz and slept 12 hours a night from 2 months on but was a pretty regular walker up to that point. My 1 1/2 we were told to wake every 2 hours to feed when he was dropping weight then after that no more than 4 hours, but he would sleep his 2/3 hours during the day, but it made him a horrible sleeper that to this day he still wakes at least once during the night and I have to rock him, and then he's up at the crack of dawn even with black out curtains. 
I don't wanna ruin her sleep if it's ok, if I really shouldn't be letting her sleep that long then I won't and I'll wake her, but I'm asking what you mommas do before we head to the dr for her weight check today.