It does sound as though you may have an infection, which this can lead to a canker sore. Of blister type bump which can pop with white pus and a bit of blood. Or if this is bone from previously as you indicate, then the pressure to the gums can also produce these white bumps. Antibiotics should help, but this tooth does need to be looked at, as it may need a deeper cleaning, which food particles and bacteria may be down in the gum line.
However just with the way the Dentist acted and lack of sending x ray off, is not a good way to start out with a new patient. Not sure of your situation, but perhaps you may want to get word of mouth from friends and family for a different dentist. (That part is my own personal observation)
If you don't feel any relief or see any change in the next 36-48 hours after stopping the antibiotics, then do be seen again.