I have a side by side and the fridge part is not cooling well. I have to keep it at max just to maintain the temp in the high 30's. Any suggestion to problem?

It's there ice build up in the freezer side at the bottom. Frost on the back wall. Yes? Defrost the freezer completely. Plug it back in, if it works for a week or so and the same thing happened again fix the defrost sys.( heater or defrost module.)