First, kudos to you for choosing to BF!! I know food allergies passed through breastmilk can be frustrating, but they are usually outgrown within a few months. Have you seen an improvement since you cut corn?
You'd be surprised by the things that can cause a reaction in babies - over the years (I think I've nursed for a total of 6 years, 1 month for 3 kids and am still nursing my 24 month old), I've had to cut chocolate, milk, cheese, broccoli, soda, caffeine, tomatoes (and all tomato based products), onions and probably a few I cannot even remember!
It's a small sacrifice to make for the ease of breastfeeding, but it can be frustrating. If I were you, I'd cut corn, see how it goes and then, in a month or two, try it again to see if anything happens. They can outgrow an allergy suprisingly fast - other than onions, I think I only had to cut items for 6 months to a year.
Good luck!!