Do you have a package or room only reservation? If you have a package, it should arrive soon. I've gotten mine as late as two weeks before my vacation began. They don't mail them until after the deadline for your final payment has passed and you have paid in full.
If you have a room only reservation, you will not get a packet from the WDTC. You will only get a mailing from DME with your vouchers and luggage tags.