What temp are you fermenting at? You've lost gravity, so I take it that the cider is fermenting. What is the size of the batch, and how much yeast did you use? Did you pitch the yeast straight to the must, or make a starter?
I have 3 gallons in a 5 gallon carboy, pitched with a starter from two packets of Notty, fermenting along just fine at around 65°.