My dog had an undiagnosed thyroid problem. It is worth having blood tests. BTW, doctors are as behind in diagnosing low thyroid in dogs as they are in humans. If you can find a holistic vet, I would take your pet there. Even with a holistic vet, you may meet resistance. My dog didn't meet the lowest threshold, so my vet didn't want to prescribe. Instead, she said that she would re-test in 4 months. If there was any drop in his thyroid levels, she would prescribe. There was a drop in the next test results.
All his symptoms remedied themselves with a small daily does of thyroid. It made a huge difference in my dogs energy level and disposition. He had become was very lethargic, and his coat was much more dry and brittle.
BTW, he had his "surgery" late in life, and had experienced a couple years of normal cycles.
Justitia