Transitions take time. Allow yourself to adjust to the empty nest. I mourned for a while, but then DH and I came to enjoy it. I did have to get a lively cat to add a bit of spice to our house...one that wants to play and craves attention.
Something that helps me when I'm not motivated is a deadline. Sign up for a swap on this board. Or make a small wall hanging or something to donate for a fundraiser. Make a baby quilt for someone due soon...whatever it takes to give you a deadline to work toward.