OK hughes41 - this is what you need to do:
Use the Sandrena every day for 16 days and continue with the Sandrena every day. Day 17 start taking 2x Utrogestan pills before bed for 12 days (it may make you sleepy so only take this before going to bed). A couple of days after you finish taking the Utrogestan, you will back just using the Sandrena, you should get a withdrawal bleed, like a period, for a few days.
This can be a very good HRT regime, so I hope it works well for you. If you find the Utrogestan make you too sedated, then I'd ask to switch to Provera. DG x