Please, please, everyone- the diagnostic info. received far outweighs the risk of the very tiny radiation dose in a mammogram.
However, it has been suggested that routine mamms should be every other year if not every 3 years.
In the 90's, I worked in a "one stop" clinic. Staff were radiographer, radiologist and breast surgeon. First of all, mammogram. Films then examined by radiologist, who, if deemed necessary did untrasound. Then if necessary, a fine needle biopsy by the surgeon.
Unfortunately, these clinics no longer exist as far as I know, but I am sure that they saved the patients a lot of sleepness nights worrying between appointments.
Also, if you have symptoms, and get an emergency appointment for a mammogram, do insist that you have an ultrasound examination too.