Resources not loading in APK

In my project, at the end of each level I am loading some prefabs and changing their sprites. Prefabs are in "Resources" folder so I access them by using Resources.Load method. Everything works fine when I run the game in Unity but when I build the project as .apk, it doesn't load prefabs and change sprites. I made some research but couldn't solve my problem. It is a critial point in my project so I have to solve this. Can someone help me?