I have been experiencing similar side effects on this drug—joint pain, stiffness, weight gain, exhaustion. I went off of it for a few months and started feeling like myself again. The oncologist prescribed exemestane as a replacement and a couple months in, I was experiencing depression, which I have never struggled with, so I went off that, tests were done, now back on anastrozole (3 mos). Just like you, my symptoms seem random, some days tolerable and other days really difficult. I exercise daily, am getting acupuncture and massage (every other week), eat well... none of this is helping much. This drug is only offering 6-8% protection against recurrence and maybe it's not enough to justify the daily misery. My quality of life is sorely depleted.