Found a New Lump After Breast Cancer Treatment: Seeking Experiences

I'm 11 months post treatment, originally had a lumpectomy of my right breast followed by chemo and radiation. However, I very recently found a lump in my left breast. I'm scheduled for a diagnostic mammogram and ultrasound this coming Wednesday but my nerves are getting the best of me. I had my I initial survivorship mammogram the first part of February and it was clear. Now I have a marble sized lump in almost the center of my left breast beneath the lower part of areola. I honestly probably would not have even felt it if I hadn't just lost some weight. My boobs are the first place I lose weight and they kinda deflate, lol, which allowed me to feel it. I was postmenopausal before I had my first cancer and I know there are other things that it could possibly be, but given that the first cancer was triple negative I'm not very hopeful that it will be something else. I'm trying not to even tell anybody about it until I find out for sure what I'm dealing with because I don't want to cause anybody undo worrying. Has anyone else had a tumor or something else grow in that general location? From what I've read it's not the norm.