In order to make yourself feel better, take him to the vet for a FULL physical and blood work and explain to the vet your worries. It might be the weather, but maybe not. Mine can go forever in hot or cold weather.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD