change of treatment meds

seen to the Onc this week for my 6 month check up. Ive been on tamoxafen for 12 months now, thought I have been tolerating the side effect ok. I had most of the side effect they talk about,  he has taken me of T and now putting me on anastrozole. Said have a 2 week break then try anastrozole for 1 month. 

I was wondering if there is any difference between side effect on these drugs and will there be any noticable within a month? 
feel a bit confused about the swap of drugs!!!!