Hi Gay, I'm 32 and just started on tamoxifen a few months ago. I too have been taking an antidepressant for a number of years and was happily stable on it. Unfortunately, they changed it when I started tamoxifen and I have been struggling a great deal with symptoms of anxiety and depression these last few weeks.
The treating psychiatrist told me that tamoxifen can actually cause the symptoms I'm experiencing! If I could have my time again, I would delay going on tamoxifen and find out more about the antidepressants I could take with it. I would then (maybe) change antidepressant and only go on tamoxifen once I was stable on that - giving it a fair bit of time, say 2-3 months.
The oncologist put me on tamoxifen and didn't say anything about what to look for in terms of psychological side effects and the psychiatrist neither. I wish I'd had more information and time to make a sensible choice - it all felt very hurried.
Ultimately, tamoxifen may be what stops you getting breast cancer again, but is it worth it at the expense of your mental health? There's much to think about, sending you my best wishes x