HonuKaha26 I'm sorry to hear of your diagnosis. It can be really confusing trying to make sense of it all over the few first weeks and months.
Have you met with a medical oncologist to receive your Tamoxifen prescription? I'm wondering because your steps are different to what I had. I had surgeries first, then radiation, then started Tamoxifen.
I have read that some types of medications have to be paused for surgery so if your surgery is soon (did it get classified as being required in 30 days?) then I myself would be double-checking with the medical team about the need to start Tamoxifen before surgery unless they've already given you reasons to start it. One of the potential side effects of Tamoxifen is blood clots.
No one can be sure of the side effects that each person will have or the extent of them. Tamoxifen can mimic menopausal symptoms and I would suggest discussing your current symptoms pre-Tamoxifen with your medical oncologist so that they can be monitored. There are options available if the side effects are too much.
For me personally, the first week of Tamoxifen was fine, then I had about a month of many and intense side effects, then over the next month they eased off. How long this lasts is anyone's guess but if they start getting worse then I'll speak to my medical oncologist again.
This BCNA article might provide some more information for you: Side effects of hormone-blocking therapy
Hopefully some other people will chime in, especially if they did begin Tamoxifen before surgery, to provide their experiences.
All the best with your surgery.