Tiredness after radiation

About 1 month ago, I completed  7 weeks of radiation therapy for breast caner.  I find that I am more tired now than when I was having the radiation (no chemo).  The first week after completion of therapy, I felt wonderful and then it really hit.  Why does this happen?  What is going on in my body to cause such a lack of energy?  Would an iron supplement help.  How about acupuncture?  I find this lack of energy depressing and debilitating.  Any helpful hints and how long does this last.  Most importantly, why?  Thanks.

[CCF-RN,MSN-JS]

Dear MSH, You have been through a lot in the past few months.  First the surgery, then the radiation therapy, this all takes it