I Had A Tooth Filled A Couple Of Months Ago.

I had a tooth filled a couple of months ago. The nerve is showing. I was told to brush with Sensodyne toothpaste. Pain is still really bad. I am feeling like my dentist may be incompetent. Does a tooth get filled if a nerve is showing? Should I have been given an option of having it pulled rather than being filled. Is filling a tooth with a visible nerve showing a normal procedure?