Have you just been prescribed new glasses? You may have an allergic reaction to the bit that sits on your nose (some people get this with earrings. watches, bracelets etc).
If not have you changed your diet recently and started eating something you don't usually eat?
Last thing to consider ~ have you got / had a cold and used tissues? They sometimes have perfume or balm in them that may be causing a reaction.
If none of those are relevant, then ask your doc for advice