Yeah - I just did some seaches and it seems that common side effects of both Arimidex and Nolvadex include fatigue. I have been taking the Nolvas for a week and I am feeling very lethargic. I don't have any hands on experience with the Arimidex though. I will be getting some soon and will post it if I experience anything.
I don't think it's the arimidex my friends. I am sure that it would be low estrodial levels. Taking arimidex every day depending on the amount could drop your estrodial levels to a point where you feel fatigued and have achey joints. You should get blood work done and see where your levels are. Go to privatemdlabs.com. Find the test for females(all the hormone tests in this panel is all you need) and look online for a discount code. Pm me if you want more info.
I read about this all the time in other forums as well as personal experience. I use krill and fish oil for achey joints by the way