I could never express milk from my bitch but all her puppies thrived. :)
I too was worried that she might not be producing milk but puppies seemed to be very happy.They fed regularly and were producing wee and poo.

You should remember that puppies,like human babies can lose a bit in the first day or so and then gradually gain it back.
How are puppies? If they are making lots of noise and are restless,then this would suggest she has no milk,but if they are quiet,warm and seem content then I would think they were fine.
Good luck and keep us updated.