New mother behavior

Question
Our shihtzu gave birth to 5 pups, three days ago. Yesterday she started sitting outside the whelping bed growling and whining before she gets in to care for the pups. Also she started going to the couch, which she had the pups on, smelling, digging like she is looking for something.

Answer
I am sure what the question is here but if this is her first litter then yes, this behavior is not unusual. It is not desirable but it is not uncommon.
As long as she is caring for the pups, feeding them and cleaning them, then you probably don't need to worry about it. She smells something on the couch is why she is rooting around on it but if there isn't something there then just remove her from it.
Has the vet looked her over since she gave birth? She might be uncomfortable for some reason. She might need a clean out shot or she could have a sore teat.
If she is doing fine otherwise then just reassure her when she is out of the box that she is a good mom and she should settle down. Watch her with pups for a while because you want to make sure this behavior doesn't escalate into puppy killing.

How old is she anyway? This is the kind of thing we usually see with dogs under two which is why it is recommended not to breed under two years old.