We usually suspect an infection with foul odor. Therefore a visit to your gynecologist or local clinic would be warranted as foul odor from menstrual periods oftentimes indicate bacterial infection especially if the patient is having fevers, nausea, vomiting, abdominal pain, or pain on urination. You should not wait until your period is over before visiting the doctor and over the counter yeast infection creams are not helpful for bacterial infections.
A foul odor during your menstrual period is already an indication for an immediate evaluation by your gynecologist. If your periods are usually on regular interval and the latest one was 6 days late, then that is an issue that should be evaluated by your gynecologist as well on your visit as it could indicate a uterine abnormality abortion (infection, anatomical defect), or even a spotaneous or septic abortion.