Symptoms Rear Shoulder And Shoulder Blade Pain 2 Yr Old Yorkiepoo With Unusual Symptoms- Stiff Rear Legs And Nausea For A Couple Days Then Completely Fine?

2 yr old yorkiepoo with unusual symptoms- Stiff rear legs and nausea for a couple days then completely fine? - symptoms rear shoulder and shoulder blade pain

I have 2 years Yorkiepoo, which is a recurring problem. 4 times in the last 4 months, a dispute with his hind legs very stiff had (permanently running) and got sick the last 2 days had symptoms. But whenever there in a few days and return to normal daily activities OK. What can be symptoms that seem so fleeting cause disappear within a few days. The vet has more than what the evidence. Please help!