In your profile, look at "Paid Subscriptions" yours expired in December. Since we use a subscription system for this, your membership expiration will be one year from when you paid last (It is not based on calendar year). You should have received a notification 10 days before expiration. You can also setup a subscription through paypal that will automatically renew. The easiest way to renew now is to just use the Paypal that you will see in the "paid subscriptions" page of your profile.