Help! Somethings not right with my baby...

  
Sophie

Sophie is always- laughing and- smiling
 
 
Barked: Tue Jun 10, '08 9:34pm PST 
confused
Hi everyone. This picture of Sophie sleeping although rare for most Aussies is becoming the norm for my girl.
She is 8 years old. Her litter mate Cooper still acts like a puppy. Sophie used to walk miles and miles with us and love it. She cannot go very far these days. She starts out strong, but tires quickly. If I walk her too far she gets very stiff after the walk. I have gotten blood work done, all negative. I started her on Syn-Flex for the past three months. The vet says she has a slight inflamation in her front paws.
It seems since this breed live to 13, she is much too young to be tired all the time.
Does anyone have a similar experience or advice. Any spectacular vitamins, special tests etc....
We want our Sophie back to normal and are very worried.
Thanks in advance.