I am not sure if I can reassure you but I can certainly empathise with your feelings which might be helpful if you know others feel the same as you,
I was diagnosed with triple negative breast cancer in February 2015. I had eight sessions of chemo after that I had a lumpectomy and month of radiotherapy.
I have had my firs mammogram giving me an all clear with the caveat that because I have dense breasts I have to be vigilant.
I saw the surgeon as a routine check up six months after my lumpectomy (2 was ago).. As a result of this she has requested an ultrasound scans because of thickening in the upper right quadrant area as well as under the arm. It can be due to scar tissue.
With exactly the same feelings and concerns as you I want to reassure you, you are not paranoid we all go through the same anxiety regarding fibroses lumps and/or pain.
Hoping everything goes okay on Tuesday. Let us know how you get on. My scan is on Friday!
Never ever feel worried about being paranoid. You've been through a lot and it's normal to be anxious X