My little Chi Chi is not acting right?

I adopted a Chi a week ago. The cutest little female...Chi Chi is her name. She was so loving and full of energy. And then yesterday as I was holding her, I moved her a little and she yelped like in pain. We couldn't figure out what was wrong. And then she just shaked so badly. She had a rough night sleeping too. Today she seemed a bit better. But I was concerned and took her to the vet. The vet checked her out, watched as she walked and could not determine the problem. Then this evening, the little one is in the same condition as yesterday. She wants to be held and really shakes. If I put her down, she'll lay down but she stares straight ahead. I really love this little girl and I want her to be well. Has anyone else had a similar situation with their pet? One more thing I need to mention... my mother in law is on Xanax and I dispense her meds. I had one on the laptop when I was browsing the web on Sunday. When I went to give it to mom, I noticed that is was dry and flaky, almost as if it was disolving. It could be possible that while I was holding Chi Chi when I was on the computer, she may have been licking it, but I would think the whole table would be gone. It was about half gone and the dose is the lowest there is.

Hopeing someone can help!!