I have had the same thing! I thought it was just me.
I have been on Prostap for 5 months and have had the usual symptoms - hot flushes ( getting a bit easier now) ; muscle and joint aches, and a higher heart rate ( about 10 bpm up). Plus this strange tailbone discomfort. I can't put it down to being more sedentary , cos i'm not ( lockdown hasn't really affected my daily activity- if anything I am spending less time in the car , and more time pottering about).
I haven't been able to find anything which either predicts or explains this. So I can't help much, other than to say- you aren't alone!