For the last month he has noticed increasing muscle and joint pain, pretty severe fatigue, memory problems, and some sleep issues (which we thought were conquered now). He also exhibits some shortness of breath, which is new. After his last infusion, he had diarrhea for about a day, which is also new. His blood work is largely okay except for hypogammaglobulinemia, which is not new.
I suggested a thyroid test, he had it done. The results were low normal, not out of range, though. The nurse at his oncologist's office said the memory thing was probably chemo brain. I didn't think immunotherapies like Darzalex could give you that, but of course I have been wrong before.

We're left with the choice of continuing, though my husband dislikes the way he feels, stopping and trying the next thing, possibly taking a break?, checking other body systems to see whether something new is causing this. Our cancer doctor is not usually a real help with stuff like this, to be honest.
Is it common for Darzalex-related side effects to occur with such a delay after starting treatment with the drug? How concerned should we be about the side effects occurring at this point?