Your agency can easily be the problem.. Do you know for a fact that they are actually scheduling you with the hospital? Some do not, and wait until they get a call from the hospital....you think that you are scheduled but you are not......perhaps you should consider another agency.
This past weekend was a full moon and most nurseries, at least Level III, were going crazy. I can also work Level III and had no problem getting placement.
You may want to check out some of the Peds ICUs in your area also, as they still get the little ones. If the infant has gone home but needs to come back to the hospital, they will go to PICU, not NICU. Something else for you to consider and you may find more extra work that way.
Good luck...................