How do you know if your allerrgic to mozi bites?

Mosquito Bites. When the mosquito bite, it injects some saliva to prevent blood clotting while it feeds. The bump you get after is swollen or itchy, and is a reaction to the injected proteins. This reaction is "allergic" like. The more you are exposed to the mosquito proteins, the more likely for some to have larger, more swollen, and more itchy bumps. These have more allergic component. No bump, no allergy.
Swelling and redness. I imagine you mean mosquito bites? Most are sensitive to these insects and have redness and itching at the bit site. More severe allergies are characterized by hives or even shortness of breath and swelling all over. Your doctor, especially and allergist can perform tests to see what allergies you have.