Hi Dollydream
from me too
In addition to the points made by Mary G and Dancinggirl - you did say that you had gone almost a year without a period - so it could be that you weren't actually post-menopausal when you started HRT and the breakthrough bleeding might just be your own hormones breaking through.
I do agree though that the more likely explanation is the oral HRT, having aggravated your digestive system and your IBS, is then affecting the absorption so that progestogen levels fluctuate leading to the sort of bleeding you are experiencing.
Also the reason why you didn't get any in the first month was probably because your body had been without oestrogen and so took a while for there to be any lining that might shed at all.
I would definitely go for transdermal HRT - and I agree you could try Evorel conti at first, but if it doesn't control your flushes then as she suggested you would need to go for separate oestrogen/progesterone or Mirena coil to enable you to increase your oestrogen dose.
Hurdity x