What happens if i'm allergic to cats, what else am i allergic to?

Varies: Each person's immune system is unique. It reacts to the environment uniquely as in how each of us has unique features. However, when you are allergic to cats, the chance is you would develop allergies to many other environmental allergens too. The only way to know exactly which one you are allergic to is to do allergy testing. A local allergist could help you figure it out.