A lump that comes up that fast could be a cyst or, given the swelling, an abscess.  The most likely cause of a hot, swollen breast is some type of infection, but a remote possibility would be inflammatory breast cancer (IBC).  Some women do experience pain after a mammogram, but usually less than a week later.  Call the doctor and ask for an appointment.  If he or she thinks the lump is a cyst, an ultrasound will confirm that diagnosis.  If the doctor thinks it's an infection, then an antibiotic will be prescribed, and another mammogram won't be necessary.  If the antibiotic doesn't work within a week, then you will need more screening for IBC.  Usually that involves imaging tests like a mammogram, ultrasound, and maybe an MRI.  Then a biopsy is usually done.  You can read more about other possible causes of breast pain in this link.  Probably the cause will be something easy to treat, but you do need to be proactive in getting this diagnosed accurately.  My best wishes to you as you look for answers.