Need help identifying cause of symptoms and a cure: dog is shaking, burrowing, stiff/sore, uncomfortable.?

My dog is shaking and shivering, and she is burrowing under the blankets to cover her face. She has taken up the habit of squeezing into small dark spaces. She is also having trouble jumping up onto things such as the sofa. She is a normally healthy happy Shih Tzu, about 6 years old. She is normally not this lethargic or uncomfortable, which concerns me. She has had back problems in the past, but that sometimes comes with the breed. She has had these symptoms before, and we had her inspected by a vet. He gave us a homeopathic remedy/supplement and her symptoms disappeared. Now that they are back, we don't remember what the remedy was. All I remember is that it was a yellow-y powder in a gold zip-lock pouch, I think it was by Solid Gold, and the powder smelled really nasty. We put a teaspoon of it in both of her daily meals until the powder ran out. [Links are appreciated in answers when possible. Thanks everyone!!]