I am much more tired also now than I was during radiation
, like you and for me it's been several month. (I also take Tamoxifen) Often, with radiation, late effects show up as many as ten years later.
So, what I mean is that I don't know the truth about this, (and most anyone won't know for sure) but that it is very possible.
With my strange later 'stuff', I was pretty much told, "we don't know...possibly, or unlikely, or very likely".