Bearded dragon not eating?

My bearded dragon is 4 years old, and refuse to eat. He is losing weight. I feed him a mixture of grated carrots, pumpkin and a herb salad mix. He gets 2 crickets a day, which is all he eats. I also have a small bowl of dry food available at all times. He gets fresh food and water every day, but don't even wants to taste it. I already had him de wormed 3 times. The vet can not find anything wrong. he gets at least a hour of morning sun if the weather plays along. His cage is heated and on a thermostat. The warm spot is 32 degrees celsius and the cooler spot 25. He also gets uv drops once a week. Im in South Africa and it is the winter season at the moment. The seasons doesn't have a effect, cause he didn't eat in the summer as well. Please help