Vaginal Prolapse with Possible Complications: Given the patient's history of multiple urogenital procedures, including bladder sling placement and hysterectomy, and her symptoms of severe, sharp, and stabbing pain deep inside the vagina, a complication related to vaginal prolapse (such as incarceration or strangulation of the prolapsed organ) is highly plausible. The recent consideration for pessary placement due to suspected prolapse further supports this diagnosis.

Urinary Tract Infection (UTI) or Pyelonephritis: Although the patient's pain is primarily vaginal, her history of urogenital procedures increases her risk for UTIs, which can cause severe pain and are common in this population.
Vaginal or Pelvic Abscess: Given the acute worsening of pain and the presence of mild nausea, an abscess related to a previous surgical site or an infected prolapse is a possible diagnosis.
Constipation or Rectal Impaction: Although the patient denies diarrhea or loss of appetite, constipation can cause significant pelvic and abdominal pain, especially in older adults, and should be considered.

Ovarian Torsion: Although less common in post-menopausal women, ovarian torsion can occur and is a surgical emergency. The severe, sharp pain described could be consistent with this diagnosis.
Ruptured Viseral or Vaginal Artery Aneurysm: This is a rare but potentially life-threatening condition that could present with severe abdominal and vaginal pain.
Malignancy: New onset of severe pain in the vagina or pelvis, especially in a post-menopausal woman, warrants consideration of malignancy, including cervical, uterine, or ovarian cancer, although this would be less likely given the acute presentation.

Endometriosis: Although rare in post-menopausal women, especially without hormone replacement therapy, endometriosis could cause severe pelvic pain and should be considered if other diagnoses are ruled out.
Vaginal or Pelvic Hematoma: A spontaneous or traumatic hematoma in the vaginal or pelvic area could cause severe pain and should be considered, especially given the patient's history of surgical interventions.

Complete Blood Count (CBC): To evaluate for signs of infection or inflammation.
Blood Urea Nitrogen (BUN) and Creatinine: To assess renal function, especially if considering a UTI or pyelonephritis.
Urinalysis and Urine Culture: To diagnose UTI or pyelonephritis.
Imaging Studies:
- Pelvic Ultrasound: Useful for evaluating ovarian torsion, masses, or other pelvic pathology.
- CT Scan of the Abdomen and Pelvis: Can help identify a wide range of pathologies including abscesses, hematomas, and malignancies.
Pain Management: Aggressive pain management should be initiated early, considering the patient's severe pain and lack of response to previous medications.
Gynecological Consultation: Given the complexity of the patient's symptoms and history, early consultation with a gynecologist is advisable.
Surgical Consultation: If there is suspicion of ovarian torsion, ruptured aneurysm, or other surgical emergencies, a surgical consultation should be promptly obtained.