Hi klynnbagstaff
How long after your last natural period did you start HRT and which HRT are you on?
If you had gone less than 12 months then you should have been given a cyclical ( sequi) HRT which would lead to a monthly bleed. If you had gone more than 12 months then you will have been given a no-bleed one. However for some women their cycles do resume more than 12 months since their last period. Also if you are on conti HRT this can lead to irregular spotting or bleeding even if you are post-menopausal, although this usually happens at the beginning.
If your periods restart or the bleeding happens irregularly then perhaps you would be better going onto a cyclical HRT so that the bleed is (theoretically) predictable. I would mention to the doc though if you are on continuous HRT and only just getting a bleed after 5 months (if you are on conti no-bleed HRT).
Hurdity x