Refridgeration Problems....?

I have a fridge that is only about 2 years old. My freezer freezes just fine, but the bottom part only stays "cool", even when I turn it as high as it goes. Sometimes it doesn't get cold enough and water drips from the inside. I noticed the other day that water was leaking from the bottom as if it was defrosting. Can anyone seriously help by telling me what it could be. Is this a major costly fixing??