I've had a staff infection, & it HURTS terribly bad!! I, too, thought it was just a bump, but was very wrong! You should see a dr, or medical professional of some kind! They have antibiotics & a cream they can prescribe you that will clear it up. Take care of yourself, & I Hope you feel better!
You can tell or know if a bump is a staph infection or just another type of infection if it recurs or appears quickly. You should consider visiting a medical doctor or a dermatologist for diagnosis and treatment. Check out http://www.ehow.com/staph-infections/ for more information.