Autoimmune issues 7+ years out - cancer/treatment related?

Hi all,

(I'm cross-posting after putting this post in what's probably the wrong forum section - mods, my apologies, and please feel free to remove my earlier post)

Haven't posted here in a long time, but my current issues brought me back. I was diagnosed Stage III ER/PR+ HER2- back in 2011 and had neoadjuvent chemo (A/C, T), radiation, and a unilateral mastectomy. Was briefly on Tamoxifen and then tried AIs for about 2 years before quitting due to side effects. Long story short, I've been mostly healthy until recently. For the past 6 months or so, I've been having recurrent low-grade fevers, abscessing skin cysts, chronic fatigue, enlarged lymph nodes that won't resolve, and numerous minor infections. When I've been prescribed antibiotics over the past few months, I've either had allergic reactions, or they just haven't worked. I also had a reaction to MRI contrast dye, which had never been an issue before. Last week I suddenly developed a very high fever (105) and low WBC/platelets, and was in the hospital on IV antibiotics for a few days. Source of infection/cause of fever was never found. I've had a zillion tests and scans, both at my local hospital and at Mayo Clinic, and still NO diagnosis. I've been seen by specialists in infectious disease, hematology, oncology, and rheumatology, and while all agree that I have some kind of immune system issues, no one has been able to give a name to this, or figure out how to treat it. Thankfully, a lot of scary things have been ruled out, but I would really like some answers so I can treat whatever's going on if possible.

I have always suspected that this is related to my cancer or more likely my treatment, and I'm wondering if other BC survivors have had similar experiences many years after active treatment? And if so, has any kind of treatment helped?

Thanks in advance for any information.