What are my breast's sore when I take off my bra?

I just had my third child 4 months ago, I did get breast augmentation done over a year ago. I didnt have much feeling in breasts for at least 8-10 months after. I just finished my period a few days ago and took a pregnancy test and it came back negative. My husband and I have been carful. What else could it be? Every time I take my bra off my nipples hurt but if I rub them there not that sore.