oh girl, I just saw your post, sorry to hear, and yes it could be that she is in pain, I remember my little angel Prada turning into the yorkie from He*l when she was in pain, they gave her a shot before she came home on spay day and a bottle with rimadyl well I hate pain killers so i did not give her her night one and she almost bit Harry boy's head,
so I called my son and asked, he said she was in pain to give her the pills and as soon as the pain was gone she was back to be my little angel.
sorry you had to go thru this too, I guess it comes with the territory.
hugs,
Carmen in nj