I had this problem myself. Try cleaning out your freezer and defrosting, even if it is an automatic defroster. Let sit over night, and pull your refrigerater out and clean the dust from the back of it and underneath it. Then plug fridge back up and make sure you don't overstuff your freezer.
Freezer coils tend to freeze up when the heater element in the freezer becomes defective. This element is behind the main rear panel in the freezer compartment and must be replaced. When you replace the heater element, remember to also replace the heat sensor nearby, because this sensor controls the on/off sequence of the heater element.