Tamoxifen confusion

Hi,

I was diagnosed in Feb, had lumpectomy, radiation, and now on my 2nd week of tamoxifen, every one is different, but I feel very tired every afternoon, and end up sleeping for a good hour, plus the headaches, I do wonder what else it is doing to my body. The radiation also made me tired, I have always been fit, and eat healthy, but that hasn't made any difference, only now I am just starting to get my strength back, 3 weeks ago I couldnt open a can of beans?  it has really knocked me about. Michele