The type of turtle i have is a red eared slider

I dont onow what wrong with it. I havent seen it eat in 3 days and everytime i try to feed it, it smells the food and walk away like its full or something. How is it possibly full if it hasnt eaten in 3 days. Its not sick or anything because it walks around as if nothing is wrong with it and it still has tons of energy because it still swims fast