If this is a propane fridge, you probably have the temperature knob turned too high. I run mine at about 2.5. When it is set too high, the second stage doesn't get a chance to work. The first stage is the freezer and the second stage is the fridge. It may take you a little while to find the sweet spot. The mistake I made when I got mine was to turn it full cold thinking it would cool down faster but it does not. It still takes almost a full 24 hours to get cold.
The temp probe in fridge attached to cooling fins in the rear, move that as high as you can on the fins. Try also using cans only on top shelf I find the aluminum helps to balance the two extremes. This issue is not uncommon. There are more drastic measures but ive found this to be decent in getting fridge to 35-39f range without the freezer growing 9" of frost.
get a fridge thermometer from the kitchen goods section of places such as Walmart or order one from online. That way you can place it down low in your fridge and get a better idea of if it is cold enough for food safety meaning 40 degrees or lower. That is the only reliable way to see what your fridge is doing unless of course everything is getting frozen in which case you know it is below freezing temperatures.
I use a tie wrap through the loop to under the top wire shelf. The gives me the temperature in the fridge. The freezer is easy because if the contents are hard, they are frozen. I place this where I can easily see it from my normal sitting position in the van.