I apologize for the slow reply. (I was away at a family funeral.)
Let's see: My spouse had never previously had any low iron test results that I know of. And his hematocrit must have been OK whenever he had last given blood--which was usually maybe once a year, something like that. But we don't think his hematocrit dropped down to the low 30s all at once because his anemia symptoms didn't come on abruptly. It was only in retrospect that I realized, oh, yeah, he was really slow coming up the hills when we were out walking, etc.
Your theory about the potential impact of your testosterone therapy is intriguing. Maybe somebody else on the forums feels able to weigh in with thoughts, as I don't have a science background and don't want to pretend I know more than I do.
My spouse also showed no nutritional deficiencies or problems with anything other than iron.
If memory serves, I came up with the theory about how his body might be suppressing the IGM monoclonal antibody after doing various forms of internet sleuthing in medical research papers. But it was just an amateur hypothesis. I do recall reading one study where the researchers were speculating that the body does engage in certain self-protective mechanisms when abnormal cells arise, and that one might be reducing circulating iron. I'll see if I can find that paper again and post a link. I think at the time I was running searches using the terms "monoclonal gammopathy" and "iron deficiency" at the same time.
I'm sorry you have been doing worse since January and that your red cell counts have been going down. Please keep us updated. It is incredibly stressful knowing something isn't right but feeling in utter limbo as far as what actually is going on or what to expect. I'm going to be sending positive thoughts your way and hoping that your situation stabilizes or, better yet, that you rebound quickly. Hang in there.