<<What could be the problematic
food? How can I relieve the itch?
Could this be a premenopausal symptom? But I'm only 12! (in Leap
years).>>

My first instinct would be to ask these questions:

Are you eating anything different that you normally don't eat?
Are you eating organic or conventional food (with conventional food
it's
possible to be exposed to a higher amount of pesticides, etc., or even
become more sensitized to them, causing a reaction).
In which area of the country do you live?  Is the humidity becoming
lower
(in other words, what seasonal changes are taking place?)
Have you changed soaps, skin cremes, or laundry detergent?

It is certainly possible to be having premenopausal symptoms.  Some
begin
getting them much younger.  It is also possible that you are reacting
to
grain-fed meat if you eat conventionally produced beef (possibly
heightened
sensitivity due to prolonged exposure if you weren't reacting before).

Also, if you live in an area where there is farm land, there are often
chemicals being applied to the land this time of year.  I tend to have
a
very strong reaction to this.

THis is just off the top of my head for now.

Siobhan