I think sore nipples can be a positive sign of pregnancy it can also be from being intimate with your significant other, meaning possibly he/she could have been a little too rough during foreplay, but it should subside within a few days or a week, if not, a doctor is recommended.
Your body may be trying to readjust itself from stopping the birth control pills. You can also have sore nipples if you have a hormone imbalance. I have had this problem a couple of times. It should go away in about a week but if it doesn't then make an appt. With a doctor.
Soreness of the breast or nipples is a sign of pregnancy but it doesn't necessarily mean that you are pregnant. You should take pregnancy test now to rule out any doubt in your mind.