It's my understanding her in the US that a doctor can terminate you for any reason but has to notify you in writing and give you a reasonable time to find a new dr (usually a couple of weeks of emergency care at least).
We terminated people for being annoying, so yes it is common. But, it seems to me that the dr is leaving himself open for malpractice by not giving a time period to find a new dr.

Some drs just don't understand how to deal with pain, so they don't.
Sorry about your friend.