Woody, Our Dog, Has Just Started Tucking His Tail Between

Woody, our dog, has just started tucking his tail between his legs and holds the hind legs close together. He seems to be very protective of the area, but will allow us to lift his tail. On Sunday,he did have poop stuck to his tail and I was able to cut it off. Other than that, his poop is normal (not runny) . He is eating as normal and his water intake is normal.