How do I know ifmy chihuahua is done giving birth?

Usually you would have had an x-ray done beforehand so you knew how many puppies you were expecting.

Pups should come no more than 2 hours apart, if it has been 2 hours you need to administer a shot of oxytocin... if you haven't organized the shot beforehand then you will need to go to the vet.

Oxytocin basically causes contractions and speeds along delivery, or if the dam has finished whelping it helps clean out all the 'gunk' left over.