It is possible that this is Lichen Sclerosus (please don't be alarmed by the images you see if you google it - that is for untreated LS and you'll be catching yours early!). A gynaecologist can diagnose this - it's helpful to go when the cuts / sores are visible.
Have you found out what was wrong. Sound similar to my situation.
It sounds like it might be thrush, a yeast infection. Its pretty common and treatable. Small tears are common with that. The only other thing with similar symptoms is genital herpes, but that is typically transferred sexually and if you have not been sexually active then that's not typically an option.
There might be something you can get for thrush from the pharmacy, without a script. If it does not help, see a doctor and get tested.