Painful Lump

Is there anyone out there that has had a painful lump that turned out to be nothing to worry about?

I am trying not to freak out and stay level headed. I stopped breastfeeding my daughter a few weeks ago and I’ve pretty much dried up since. I’ve had a pain in my left breast since I began weaning and now I have just discovered a small lump in my upper inner quadrant that is in the deep tissue of my breast (in the same place the pain occurs). You can only feel it if you’re using decent pressure. I can’t really tell if it’s movable seeing that it’s deep. I should also mention that I’ve been having some intermittent shoulder pain and arm pain with a random pain in my back between my shoulder blade and spine that happens sometimes when I swallow and/or take a deep breath. These pains are all on the same side as the painful lump I’ve had two ultrasounds, one being before I weaned my daughter and the other was in the ER about a week ago. Both US came back “clean” but I’m wondering if the fact that I was still producing milk made it to where they couldn’t see any masses on an ultrasound. I have an appointment with my OB on Wednesday to get it looked at and hopefully referred out for additional imaging. I’m so nervous this is going to turn out to be something bad.