Four months ago, I had a cavity filled. It was a deep one that went into the pulp and had gotten to the nerves in my gums. After that, it was a bit sensitive. About a month later, I had my teeth cleaned and told the dentist that it was still sensitive. She said that was normal. Now, it still hurts when I drink cold liquids or eat cold foods. It also tends to sharply throb for a few moments, usually after I wake up. My tooth also tends to hurt whenever I hit my head on something. What can I do?