My right nostril is swollen inside. is it a pimple or an allergic reaction?

Nostril bump: Generally, pimples inside the nostrils are painful/tender, while allergic reactions are itchy. Most likely, you have a pimple or an inflamed (+/- infected) hair follicle. If your condition worsens, you develop additional symptoms, or it persists unchanged for 2+ weeks, you should see your doctor. If you develop swelling elsewhere, difficulty breathing or swallowing, ... Go to the er!

Is it painful?: Pimples are painful to touch, pushing on your nose would hurt. Allergic reactions that cause swelling in the nose are not painful.