I finished my radiation treatment (after chemo) back in early Nov 2012 and, with my oncologist's approval, waited until mid-Jan 2013 to start tamoxifen. I wanted to get through Xmas without side effects and give myself a chance to recover a bit before starting the next thing.
I was really worried about taking tamoxifen. I read so much depressing stuff online about it but it has been fine. I do get mild hot flushes but I expect I would be getting them anyway due to chemo-indused early menopause. I really don't have any side effects. I exercise regularly and try to eat a healthy diet and drink very minimal alcohol. I think all that helps. Almost two years on from finishing my treatment I am feeling great. So don't despair it might not be as bad as you fear. Good luck, Janet.