Do shrimp and melons have any shared proteins?

My mouth itches after I eat a banana, but if I cut up a banana and put it in my cereal with milk I am fine. I know it means I have an allergy to something in the banana, but why does it go away with the milk and sugar? This also happens if I eat melons (watermelon, honeydew, cantaloupe, avocado, etc). I have not mixed any of those with milk and sugar, but I know the avocado makes me itch when I eat it alone, but not when I eat guacamole. I am also allergic to shrimp (I have not eaten lobster, crab, etc for as long as I can remember) but shrimp does still bother me...much much worse than the melons and bananas. I never eat it, but I know that the shrimp juice and if it is cooked next to my food (like at Hibachi) I swell up. So my questions - does shrimp and melons share the same proteins? Thank you for any help.