My molar had a crack that has recently been filled and now had crown prep. I am worried that it needs a root canal.

Before the new filling the tooth only bothered me when biting down on hard food. After the filling everything felt great. After the crown prep it now has a dull ache and immediately hurts when I bite down on anything. Even cupcakes! My gums and cheek are also very sore to the touch. I have since seen my dentist and had xrays. He said it will resolve itself after the permanent crown is placed but I am scared the tooth has a cracked root or needs a root canal. Should I get a second opinion?