Breast lump?

A little over a month ago, I noticed that my right breast was sore, mostly to the touch or if I slept on it, but it was around the time of my period so I thought nothing of it. It seemed reasonable.

However it’s still as, if not more, sore than before and there is a rather large lump within the breast that moves around, it’s not like a small ball or so that would fit between my fingers, but a large and flat lump that feels like it’s takes up half of the breast ( I have very small boobs fyi). It kind of feels like the inside of it has hardened a bit and the top part of the lump is very sore. Yesterday I also noticed that the nipple on that side has gotten a little bit darker.

This morning today I went to the emergency room and the doctor told me there was no abscesses, no infection and no cancerous lumps, there is nothing to worry about. Although the doctor seemed a bit uncomfortable with my questions and he didn’t really feel for anything it felt like, he mostly poked on the top where I said it was most sore. Then he asked me if I used any contraception of any kind but he sort of whispered the question, which seemed strange to me.

Has anyone had a similar problem? What did it turn out to be?

Also I am going to book an appointment with my GP after the weekend.