MRI results after exchange surgery

Sorry, I'm posting in different places, just trying to get as many opinions as possible.

Background: Diagnosed 6/21/17, stage III triple negative, high risk for recurrence. Had neoadjuvant chemo (failed taxol, partial response to AC), a double mastectomy 11/27/17 (less than a mm margin achieved), radiation early 2018, Xeloda April - Oct 2018, and just had my exchange surgery 11/29/18.

Around New Year's felt a tiny lump in the same spot as the original cancer, lower outer quadrant. My oncologist sent me for an MRI and ultrasound. I was told they saw "nothing" on the imaging. (Which of course made me feel silly and crazy).

Later found out the MRI was BIRADS 2, which I understand means they saw something but felt it was benign.

Now, 3 weeks later, the lump has definitely grown. I have what I refer to as an "internal itch" feeling where it almost seems like I can feel it growing. (I had my core biopsy to diagnose, and since I was in a clinical trial, I also had 3 additional biopsies on the original tumor during neoadjuvant chemo to collect tissue samples for research. But I had radiation after my mastectomy, so I think my risk of needle track seeding should be pretty much nil.) There's another lump now in the axilla area that was not there at all when I had the MRI and ultrasound 3 weeks ago. There is swelling now over the ribs next to the lower quadrant lump and they are a little sore to the touch.

And a tiny painful spot on my sternum, very close to the rib on the left/non-cancer breast. It also has this "internal itch" feeling (exactly the kind of "itch" I felt in my original tumor when it was growing fast and I was told it was a benign fast growing Phyllodes tumor) and if I run my fingers across it, it feels like that particular rib is swollen and I think I can feel a very tiny nodular-type thing, like smaller than a grain of rice. (I can also feel what I think is the edge of the implant.)

So today I was finally able to read the actual MRI report. For the left/non-cancer side where I have the painful spot, it says: "A retropectoral silicone implant is present. Thin rim enhancement is seen in the left parasternal region, mainly involving the subcutaneous soft tissues and to a lesser extent within the underlying chest musculature. This is likely related to the patient's reconstructive surgery." Did anyone else have an area enhancement on imaging after exchange surgery? (And what "soft tissue" are they talking about? I had a complete mastectomy, so wasn't all the tissue removed?)

So now that I know the area where I'm feeling this pain is the area where enhancement was seen, I'm feeling uncomfortable about just assuming it's due to the surgery 2.5 months ago.

The plastic surgeon is saying he feels pretty confident all of this is normal post-surgical changes. I talked to a few friends in real life who have had breast cancer who didn't have any of this so I'm just looking for insight. I'd love to hear any and all opinions on this.