Hello, ive been taking 20mg for a week and a half and so far I still feel like me. Obviously it’s very early days but I was super nervous like you and expected me to be different over night. Our situation is different and I think the side effects I get arent just because of the Tamoxifen though it doesnt seem to have made them worse. I am 40 years old, I had 8 rounds of chemo and by the 7th my periods had stopped and I started to get hot flushes. I am also on Zoladex injections which I think ramped them up a bit.
The hot flushes are quite hard to get used to and I am going to invest in a good hand fan soon. On a bad day I can have maybe 8-10 and a good day only 1 or 2. They definitely can be triggered if I get emotional over something but other than that I havent noticed a pattern yet. Im not drinking alcohol and I try to only have 1 caffeine coffee a day. The rest I just have decaf. I also get night sweats but the weather has not helped.
You have been through a lot! A cancer diagnosis, a major operation and radiotherapy. I am going to say you are definitely resilient enough now to manage anything Tamoxifen throws at you 
The one thing that keeps coming up when I research how to help side effects is movement. Walk/move as much as you can. If you feel fatigued, don’t assume that’s it for the day. Try to walk it off a little bit and you might feel better. That’s what I do. I don’t mind fatigue in the evening but if I wake up and feel like that I don’t allow it. I have to walk it off. Not miles, just enough to shake it off. I.also take my Tamoxifen right before I go to sleep at night in the hope that the majority of side effects happen when I sleep.
Big hugs