Hi Amysarah
Zinc and castor oil cream will do 2 main things for you one is to sooth the are the other is to help it heal. As I said before one really knows what cause of vestibutitis but some circles suggest it could be related to infection. You would only need some very minor damage for a bug to get in and cause infection. Yes you can buy it over the counter and it is as cheap as chips.
Steroid cream will help with the inflammation.

I do know about xylocaine also called lignocaine. It is what they use when you get stitches. (often called a local). It is also in many products such as emla cream and SM 33. I am not sure if it would be ok to use on the vagina mucosa as it can cause irritation but if you want to take the chance then youst try a small amount first.
Kenacomb may help because it can help with inflammation. Again it is something that is not overly expensive so it would be worth giving it a go.