Somtimes these lumps can be caused by staph infections.
Shaving can cause them by getting a cut and then germs get into it.
They can be extemely painful and you do not want it to spread.
I agree also that the hair follicles can get clogged too. Sometimes they need to be drained by a Dr. You can put hot compresses on it evey hour or so. It should help it somewhat.
Also, certain types of antibiotics only work for certain strains of bacteria. You would't take an antibiotic that's recommended for treatment of strep throat for an infection in your lungs or for a cyst.
So even though you were on anitbiotics for a different illness, it may not cure or help erradicate the cyst you have on the inner thigh.
I hope she sceduled you a follow up apptn. Did you?
It takes a while for the medication to really start working.
Good luck on your recovery and hope the pain and lump goes away.
Linda