I think you are meant to start at least 6 weeks before your EDD, it cuts down the risk of teariung , Do use something non scented or it'll sting !! Neals yard do a lovely " mother's balm" which you can use down there or failing that olive oil - not for cooking but for skin !!
make sure you use the right type of oil.
if you have a nut allergy almond or walnut oil can cause a reaction in some cases....imagine!!
I used vitamin E oil from Holland & Barratt.
Still had to have an episiotomy (sp?) LO thought he'd come out with his hand on his head. Nice. Good luck!
I did it every day from 31 weeks had 2 boys and no tearing at all. It takes a while to get used to it but I would deffo do it. I used almond oil, which I also used to rub on my belly and boobs to reduce stretch marks. It was a bit difficult when I was preggers the second time and my ds1 hovering around all the time, saying what you doing mummy !