We own a 4 year old male bearded dragon , over the last week he has been off his greens and crickets , his weight over the last week has plummeted and today when I checked the tank his head was very yellow and he seemed very weak and couldn't keep his eyes open , phoned the local pet store and they said it could be stress , somehow I think it's more serious than that , the temp in his tank is fine and uv light is working fine ,his stools are fine too , he has little black spots on his back too , any suggestions ???