Hi PaulaF72 - I'm 47 and started on Tamoxifen five months ago. For me the first week or so was fine, followed by two months that were a bit difficult.
I went through a lot of side effects, some lasting a day or two while others persisted for a few weeks. I didn't have great sleep due to the side effects. None of it stopped me working or doing every day things. My oncologist listened to the side effects, gave some suggestions, and asked me what I wanted to do - I told him I'd keep going because it felt like the side effects weren't as strong as they had been.
The side effects began to ease so I'd only notice odd things occasionally. This past month I haven't had any noticeable side effects at all and I am hopeful that this is now how it will go from here.
Not everyone will get side effects. I was hopeful I would be one of the lucky ones but when I wasn't I ploughed on anyway and held onto some wise words I found in these forums that the side effects show that the medication is working.
All the best with deciding which next treatment path to take.