Small hard ball on breast?

So I'm twelve weeks pregnant and I was lying in bed this morning feeling my breasts, and I noticed on part of my mamory there's a small hard ball. Not exectly a lump but it doesn't feel like the rest of my breasts. I have naturally very very large breasts and being pregnant has made my mamories much easier to feel, very lumpy but squishy. This feels like its attached to the mamory but it seems more solid. If I push hard it seems to have some give, no pain with it or anything.

When should I worry?