Could be many different things. You didn't mention what type fridge you have (side by side, top freezer, etc.). I know my side by side tends to make things on the top two shelves frosty if stored against the left (freezer) wall.
Some things to try:
- The fridge gets its cold from the freezer...is the freezer control set too high?
- Set both the fridge & freezer controls to the mid-point and see what happens after a couple of days and see if new items added don't "freeze."
- Clean the condenser coils (we should do this anyways).
- Both the fridge & freezer need free flowing air circulation...are any of these vents blocked (esp. check the freezer for boxes/food blocking the vents).
If none of these things help, then it could be one of these problems & you probably need to call a repair technician:
- Problems with the damper going from the fridge to the freezer (it might be cracked or stuck open).
- Thermostat may be going bad.
- Might have a leak(s) in the door seal (causing the unit to run more than it should).
- The unit may be a little low on refrigerant or the compressor is becoming inefficient causing excessive run time.
That's all I can think of right now. Can you tell I've had fridge issues over the years?

Good luck and I hope it's something you can fix yourself.