Bearded dragon won't eat: temperature problem?

I have a 3-4 month old beardie and he suddenly stopped eating. I've been trying to give him crickets, dubias, mealworms, blueberries, arugula, etc. A few days ago, he was fine and was eating like normal, but now he will look at the food and close his eyes. What should I do? I've been keeping him hydrated and giving him his warm baths. He has a 40 gallon tank now and I use the dual heating light that has a 100 watt basking bulb with a UV light. Should I buy a UVB strip instead? His temperature is reading 80 at the moment