Soreness around molar crown?

Any opinion from a dentist would be greatly appreciated! I had a root canal and crown on tooth 15 in 2007. No problems until the last couple of days when I've started experiencing some discomfort and I can't really chew on that side now. I have NO hot or cold sensitivity, and it's not a sharp pain, but feels more like pressure soreness. It reminds me of the kind of pain after I had my braces tightened when I was young. I have an appointment to get this seen, but it's not for a few days and I'd like some thoughts as to what it could be? Is it possible for permanent crowns to shift around a little and cause this kind of discomfort? I'm scared to death that it's something bad that would require extraction. Thanks for any input!