I'm in no doubt that Utrogestan (and all the synthetic progestins) is the achilles heel of HRT and has some strange side effects and I cannot take it for very long. Stellajane, I can relate to what you are saying about it taking a few days to flush out of your system before the bleed and I think it hangs around in your body for longer than it says in the instuctions.
If you are happy with HRT but hate the Utrogestan part and it is ruining your life, my advice is this. Try taking 100mg Utrogestan vaginally for 7 days, and then go and have a scan immediately after your period. I know it's difficult to arrange, you will probably have to pay for it and you will have to book it well in advance but it is the only way you will ever know if you are taking the right amount. I did it recently and my lining measurement was only 2mm so it must be working in my case but I realise everyone is different and of course this dose might not be enough for some women but at least you will know. It might sound radical but what else can you do? I had no choice because I can't take any more Utrogestan than I do now so if it didn't work, the next step for me would be a hysterectomy.