I have a mini Doxen. Three weeks ago she started to have severe pain on her under belly. Every time we would pick her up she would yelp as if she is in a lot of pain. Now three weeks later she is arching her back as if somebody has just kicked her. She is now having a very hard time walking. She almost has to drag her back legs as she is doing this. My question is this common or do I have a serious problems. What is the best course of action?