I've never had food allergies & tested neg for them, but do have eczema & chronic hives. does this mean i'll react to big allergens like nuts & fish?

Hives: Since you have 2 of the factors for the Atopic triad, you will need to be careful regarding any foods ingested, especially nuts and seafood. If you tested negative, though that is a good sign. You should continue to maintain close contact with your allergist and also seek their advice.

Allergens: Your eczema and chronic hives may have other cause than nuts and fish

Not necessarily: In fact, your own experience with eating nuts and fish is a much more reliable indicator of whether you're actually allergic than the results of skin testing will be. I think your allergist will tell you the same thing. The best way to determine whether your skin issues are due to allergy is a few weeks' trial of an elimination diet. Ask about it.