pain under crown

[bapt]

I felt like a filling was shifting so went to the dentist. He wiggled my crown (upper molar) and it came off along with a big piece of my tooth. He said it broke above the gum line, nerve was not exposed, things looked good, so he put the crown back on using 3 posts instead of the 2 posts I had before. I felt a couple of mild nerve twinges during the procedure, even with novocaine. But things were fine until 2 days later. I drank something hot and felt a painful twinge above the tooth. I have pain off and on, sometimes mild and sometimes strong, ever since. I can't predict when it will hit--sometimes when eating, more often when not eating. It feels like the pain I had on another upper molar on the other side of my mouth that cracked below the gum. Back then I had to have an emergency extraction--no problems since.
Could I possibly have a hairline crack below the gum on this tooth? The dentist said he would order an extraction if the pain continues. Should I do this since it worked before and it won't show? I can't live like this and I'm afraid of a root canal.
Thank you.