Perimenopausal, just means 'around menopause', the same way that 'perinatal' means around birth. It usually lasts until 1 year after your last period, then they can say you are post menopause.
In reality, there is no line, it can be a long process, and hormones continue to decline for another couple of years before they bottom out.
You don't have to be snappy and testy if you don't want to be.
Read up on menopause www.menopausematters.co.uk/index.php. This is a good site, with lots of information, a magazine, which is full of useful stuff (I know it looks a bit like Peoples friend, but it is really fab, expecially the last edition with the information on the new NICE guidelines).
Get your house in order with regards to diet and exercise, sleep routine and life balance. Have a look at other methods of contraception/hrt (Mirena and patch/gel will give you bioidentical oestrogen in a nice even way, day in day. Qlaira is a contraceptive pill with bioidentical oestrogen, but phasic). Look after your physical wellbeing.
I am sure there are lots of Stately Home people who can point you in the direction of counselling/selfhelp etc.
Be kind to yourself, and it will come out right. You are your own person.