I was only on Letrozole for 6 weeks & I've only just started on Arimidex 2-3 weeks ago, after a 4 weerk break after 6 months on Exemestane @Cupcakes .... and I think I have about the same stiffness & pain in the fingers .... and the thumbs also (particularly the left one.) But in 'general' I don't seem to be as aware of 24/7 pain quite so much at this point in time (early days, I know.) And I am also on some magic oil that may be helping! ;)
I've not heard of anyone suddenly getting their period back! Definitely worth getting that checked out properly!