You may find that your fridge isn't getting cold, but the freezer is just fine. If you've already checked to make sure the inside vents aren't blocked and it seems to defrost occasionally, then the diffuser door that lets cold air in from the freezer may be broken.
On ours, the diffuser door motor pushes on a small, fragile tab on the diffuser door. The tab snapped off. Rather than purchase a new $80 assembly I fixed it with a toothpick and super glue. This fix may or may not last forever, (worked for about 3 years), but evn if yo want to rpelace the diffuser, it'll help you keep your cool until the replacement comes.