I had a root canal done in my front tooth and crowned. About couple years later, my crowned tooth broke off right at the gum line. The crown itself didn't break but half of my tooth is still inside. I got it fixed by inserting a metal post. The next day, my gum was really red and swollen but it went away after a week. Now more than a year later, i discovered a tiny white blister above that same crowned tooth. What is going on???