Bacterial Vaginosis (BV): The patient's symptoms of thin, grayish-white vaginal discharge with a strong fishy odor, worsening after intercourse, along with a vaginal pH of 5.5, positive whiff test, and presence of clue cells on wet mount, are classic findings for BV.

Vaginal Candidiasis: Although the patient denied itching, which is a common symptom of vaginal candidiasis, the presence of diabetes (especially with poor glycemic control) increases her risk for fungal infections. However, the absence of itching and the specific findings on examination make this less likely than BV.
Trichomoniasis: This sexually transmitted infection can cause a malodorous discharge, but it typically presents with other symptoms such as itching, burning, or pain, which the patient does not have. The wet mount examination would also likely show motile trichomonads if this were the case.
Atrophic Vaginitis: Given the patient's age and symptoms of vaginal discharge, atrophic vaginitis could be considered, especially in the context of decreased estrogen levels post-menopause. However, the specific characteristics of the discharge and the positive whiff test are more indicative of BV.

Pelvic Inflammatory Disease (PID): Although the patient's presentation does not strongly suggest PID (which typically includes pelvic pain, fever, and other systemic symptoms), it is crucial to consider PID due to its potential for severe consequences, including infertility and chronic pelvic pain, if left untreated. The patient's history of inconsistent condom use increases her risk for sexually transmitted infections, which can lead to PID.
Cervical Cancer: While the patient's symptoms do not directly suggest cervical cancer, any abnormal vaginal bleeding or discharge in a woman, especially with a history of inconsistent condom use and potential for untreated sexually transmitted infections, should prompt consideration of cervical cancer. However, the specific findings in this case are more suggestive of an infectious or inflammatory process rather than a malignant one.

Desquamative Inflammatory Vaginitis (DIV): This condition presents with a purulent vaginal discharge and can mimic other vaginal infections. However, it is less common and typically includes symptoms of vaginal pain and burning, which are not present in this case.
Vaginal Tuberculosis: Although rare, vaginal tuberculosis can cause abnormal vaginal discharge. Given the patient's other health issues and the fact that tuberculosis can affect anyone, especially those with compromised immune systems (like poorly controlled diabetes), it remains a rare but possible consideration.