Congrats on being cancer free!
My oncologist had me on a pretty close regime to what you have gone through, 6 months of chemo, double mastectomy (mid June) although the reconstruction was delayed a few weeks (end of June). I had been taking the keytruda while on the chemo, but during surgery they stopped giving it to me and I just started again last week . I have not had any side effects so far from it, knock on wood, I do take a probiotic supplement but other then that I haven't changed much. I have 8 treatments left, and they are 3 weeks apart :).
While the chemo did not knock the cancer out, the mastectomy did and I also got the all clear 🙂