After cleaning out Dragon, return to the Medicine store and replenish the medicine supply.  Now go outside and start using your whistle to warp to other labyrinths.  If you do this correctly, you should now be in front of the Moon Labyrinth.  Now go south from there and then east.

Link should be in a forest.  Look for a scene where one tree in a line of several that can be touch from both left and right.  Use the candle to burn it and a passageway will open.