Why doesnt my red ear slider turtle eat hes about 1 year old he use to eat worms pellets minnows even hot dogs now he doesnt eat at all its been about 3 weeks please help?

There could be a number of health problems. Internal and external. First, look for any possible scratches that could be infected. Many turtles will develop sores from where they rub on the plastic or glass of a tank and if left untreated, will become infected. Turtles are like many reptiles. If they eat a big enough meal, sometimes they won't eat for days, even months. My snapping turtle went a whole 6 months without eating. Water temperature could be a factor. Turtles are sluggish in cold water and extremely agitated if the water is just a degree above comfort. And They become bored with their food very fast which is why it is suggested to feed them a variety of food. Stress could be a problem. If you moved anything in the tank or pond where he is kept, he may not like that and would probably like the habitat the way it was. Hope this helps