During lunch and dinner, i ate chicken, and after eating, my nose got itchy and sneezed several times. 2 weeks ago, my nose got itchy also after eating shrimp. can it be because i'm allergic to it? after all these years, i just discovered it lately?

Maybe/not. What else were you exposed to in these settings. Some pollen in the air, a seasoning on the food? Something you drank? Food allergies do occur and can be acquired as you get older but they are hard to pin down. Excluding a food from your diet for a week & re-introducing it can often confirm/exclude the issue if symptoms are minor.