Regarding the Tamoxifen...
It takes around 2-3 months to build up the working concentration in your blood, so you might not see any improvement in just 3 weeks. (I think that could be solved with initial dose escalation, but that's not something that oncos ever do.) This is not a problem if you start the tamoxifen at same time as the bicalutamide, because the bicalutamide takes approximately same length of time before any signs of gynecomastia (breast growth/pain) are likely to appear, but if you only start taking tamoxifen in response to gynecomastia, it might take a while to start working.
1 x 20mg/week is half the recommended dose of 2 x 20mg/week for gynecomastia, so it might not be enough to have much effect.
Some peoples' livers don't like Tamoxifen, and a swollen tender abdomen could be an issue with the liver (although at only 20mg/week, I really doubt it). However, it might be worth asking for a blood test including full blood counts and liver function test, just to check. It's a good idea to request that after you've been on Tamoxifen for 3 months anyway, because usually there are no signs your liver doesn't like Tamoxifen.