Hi scoobylyn
You are most likely to be bleeding because the womb lining has built up and is coming away due to the initial dose of progestogen from the patches - bleeding is common in the early stages of continuous combined HRT. Eventually the progestogen in the patch will stop the lining developing and then the bleeding should stop. Unfortunately this can take up to 6 months. Personally I would always suggest to women in your position who haven't had a period for a while, to go onto cyclical HRT to start with, which would give 4 week regular withdrawal bleeds, and then if you are OK on the progestogen, switch to the continuous combined, when most of the lining from the previous few months (if any) has been shed. However many women do just fine on the regime you are doing - but you might just have to put up with bleeding for a while longer.
If you are definitely post-menopausal ( at least 12 months without a period) then it is unlikely that it is a natural period ie your own hormones - but a small proportion of women will continue to ovulate occasionally even after 12 months without a period.
At the moment it is nothing at all to worry about, but if you continue to get bleeding after 6 months or it is very heavy for a long period of time - then do get checked out or earlier if you are worried. You may well have a 3 month review anyway so you can mention this then?
Hurdity x