Even after menopause, our bodies still produce estrogen through the adrenal gland and fatty tissues. So when you take any anti-estrogen pill, it blocks this estrogen that is being produced. Since estrogen sort of keeps our moods regulated, we can have mood swings when the estrogen is blocked. However, the body is like an amazing machine, and it adjusts over time, so please don't go off the anastrozole. Give your body time to adjust. The symptoms you're experiencing should decrease. Hope that helps.
Hugs & prayers,