Hi and welcome to MM
Your story is not unusual and it's great you have been given treatment that is helping. You have essentially been given progesterone which will help stop the womb lining from building up while you are still in peri menopause - essentially, though you had stopped having periods, your body was still producing oestrogen and this is why the womb lining had built up and this is common in the peri meno stage. Many women have erratic, heavy or problematic spotting and bleeding through peri meno and this can be alarming as we are not educated about what to expect when menopause starts.
Once your oestrogen levels do drop, then the progesterone you have been given, will not be appropriate on it's own, as it will over thin the womb lining which could cause other problems, so I hope the doctors will monitor this and you should query this in a few months time. Many women with problematic bleeding are given a Mirena at this stage and then oestrogen can be added in as the oestrogen drops or when flushes etc start - you might want to consider this. I'm sure they have done blood tests to see what your FSH and oestrogen levels are?
You may be lucky and not get too many flushes as your oestrogen drops - not everyone gets extreme meno symptoms - so don't look for problems.
Do read up all the info on this site to get clued up and hopefully you will stick with what you are doing for the next few months and then, when you stop this progesterone, you will be fine.
BTW - breast cancer risk before 60 is very, very low on any hormone treatment -the leaflets just have to include this. Alcohol, smoking and being overweight are far more dangerous Dg x