JustWanna, another thing to look at, if they both get sore, but one more than the other, chk your caffiene intake. Some women continue to lactate a tiny bit, but it does need to be chkd out.
The breast tissue changes as we age and changes alot during childbirth, etc. It could be too much caffiene and fibercystic breast tissue. But if only one is sore and the other is perfectly normal, I would suggest getting it chkd soon. Could be an infection. Ussually, pain is not associated with really bad breast issues...normally...that is not to say it cannot be.
Another thing too, if you are still with a partner and have been the entire time, it could be that stimulation to the breast, ie...during sexual activity or while sleeping ( if it is the side he cuddles in his sleep) could keep it stimulated just enough to keep a few glands active.
But, ultimately it needs to be checked by your Dr. For a definate answer.
Beer consumption will keep the milk glands active too.