Re the 12 days - as already discussed if you are late peri and don't have a regular cycle it doesn't matter when you start but it is 12 days in the 28 day cycle. It doesn't matter how you number the days - it's just that the convention with a 28 cycle is for Day 1 to be the bleed so that's why utrogestan is prescribed from Day 15-26. If you are already taking oestrogen then if you want you can call the day you start the utrogestan as Day 15 so that you can work out when your bleed comes in relation to when predicted!
What dose Cyclogest have you been given? I used this for 4 years and I think when I first started utrogestan was not yet available - Cyclogest was the only progesterone.
For those who want to know this has been around for years as a natural progesterone for fertility - it comes as waxy pessaries which can also be used as suppositories. It isn't licensed for HRT although some gynaes ( and my gynae specialist GP) prescribed it for this purpose. The usual dose is twice as much as for Utrogestan so for a cycle you chould have been given twice the number of 200 mg capsules. I was prescribed 400 mg for 11 days per 28 day cycle. Mine came in 200 mg capsules so I used to put one up the front and one up the back
(interesting effect the next morning!). I did feel that this was too much progesterone but it seemed to produce a withdrawal bleed OK.
Re the doc saying use for 12 days and 3 days break. Did the doc suggest you then had another 12 days? If so as others have said this is totally wrong!!
I agree with Dancinggirl re starting with 50 mcg as there are fewer side effects - would be good to be on 100 mcg eventually at your young age though. I was given 50 mcg but I was late peri and nearly 54. I sometimes wonder how I would have felt if the dose had been increased. Probably too late now at 62!
Hope it goes well for you.
Hurdity x