Why won't our sure flo water pump in our rv pump out water?

I turned the switch on and used the water once for the toliet and sink and it worked fine. I left the switch on (not sure if I was supposed to or not) and came back three hours later and now the pump seems to be working but no water comes out, we only here a gurgling noise of water. We are at the EAA Fly In and could use some water :) Thanks!