Sorry that you are having these side effects, @tessg - I've been on it 5 years now & am going OK - just a few aches now & then, mainly & sore feet!
Contact your Onc/Breast Care Nurse now & let them know - you may be able to get an earlier appt to see the Onc, assuming you wouldn't be seeing them now for a few months? I only lasted 6 weeks on Letrozole, then 6 months on Exemestane, before changing to Anastrozole, which ended up being the best one for me.
Everyone reacts differently to the different AIs, some have side effects, others just sail thru it blissfully unaware of side effects (lucky them!) .... As @jennyss suggests - gentle exercise like walking could be good for you, if you are able ....
Take care, all the best ..