Hi Tink
Firstly, have you been to see a gp about this? It sound like it could be thrush (a fungal infection), which can start when the flora of your vagina becomes unbalanced.
It could also be a type of dermatitis, usually from soap (even the type of washing powder you use as residue / perfume can remain after washing towels, knickers, etc). I had something similar in my twenties, used to come and go, it was soooo itchy, and finally was prescribed a type of steroid ointment with strict instructions on how to use it. Also instructed not to use soap or scented loo paper and to be careful of the washing product I used. And I haven't had it since, except if I've been at a friends, and they have scented paper, but I know how to manage it.
If it's vaginal atrophy, you can get an oestrogen cream or pessary to help with thee symptoms.
So get your gp to have a look, test it if they need to and sort it out!