Any suspicious lump or malformation should be addressed to your doc. It's best to get things checked out early rather than wait.
Having said that, I'll also add that there are many changes to the breast and the body that occur during a pregnancy. One is darkening of the areola in general, and also enlargening, etc. This is different for all women, I believe. I'm not sure of the lump that you speak, I can't see it, and you probably couldn't describe it enough for any of us to make a good guess. I know that doesn't help much.
Best of luck, try not to worry until you know for sure there is something worth worrying over. Easier said than done, I know. Congrats on your pregnancy. I hope the remaining time is easy and uneventful for you and the baby.
This really is a questions about breast cancer btw. Which is the first thing I considered when seeing it, but thought I should give all the information above here.