Ovarian Cyst or Torsion: This is a common cause of LLQ pain in young women, especially when associated with nausea. The absence of fever, chills, or diarrhea makes an infectious cause less likely, pointing more towards a gynecological issue.

Constipation: Although the patient does not report diarrhea, constipation can cause significant abdominal pain, including in the LLQ, and is often accompanied by nausea.
Irritable Bowel Syndrome (IBS): IBS can cause abdominal pain and nausea, and while it's more chronic, exacerbations can present acutely.
Diverticulitis: Although less common in younger patients, diverticulitis can cause LLQ pain and nausea. The absence of fever and chills does not rule out this diagnosis entirely, especially if the patient is early in the course of the disease.

Ectopic Pregnancy: Although the patient's presentation does not specifically suggest pregnancy, any female of childbearing age with abdominal pain should be considered for ectopic pregnancy, which is a life-threatening condition.
Appendicitis: While appendicitis typically presents with right lower quadrant pain, it can occasionally present atypically, especially in women, with pain in the LLQ.
Intestinal Obstruction: This is a surgical emergency that can present with nausea, vomiting, and abdominal pain. Early diagnosis is crucial to prevent complications.

Endometriosis: While endometriosis can cause chronic pelvic pain, it can also cause acute exacerbations, including LLQ pain, especially if there are endometriotic implants in the bowel or on the ovaries.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause LLQ pain and nausea, though they are less common and typically have a more chronic presentation.
Ruptured Abdominal Aortic Aneurysm: Extremely rare in a young woman without risk factors, but this is a life-threatening condition that should be considered in the differential diagnosis of acute abdominal pain.