What is a smelly discharge after your period?

Vaginal odor. Blood in vagina gets broken down into into products which gives the odor off when interacting with normal vaginal bacteria. If odor persists with discharge, one must rule out retained tampon or other vaginal infections needing treatment like bacterial vaginosis.
Infection. There should never be an odor from discharge in the vagina. Any bad smell could indicate an infection of the vagina, cervix or uterus. If you have this symptom you should be seen by a gynecologist or family physician to determine the exact cause and appropriate treatment.
Old blood and tissue. Blood may break down and cause an odor to occur. Sloughed off tissues from the wall of the uterus is exposed to air and starts deteriorating along with the blood to give a distinct odor.
May be normal. Discharge with odor may be result of residual light flow. Try a tub bath or douche after menses. If no better consult md.
Vaginitis. A lingering odor after your discharge is likely a bacterial vaginosis infection. This is not an std, but an infection caused by a change in the vaginal ph. See your doctor for antibiotics. An odor could also be trich, an std. See your dictor for testing an treatment.