Appendicitis: This is often the first consideration for lower abdominal pain accompanied by fever, especially if the pain initially presents around the navel and then shifts to the lower right abdomen. The fever can indicate an infectious or inflammatory process, which aligns with appendicitis.

Urinary Tract Infection (UTI): Lower abdominal pain and fever can be symptoms of a UTI, particularly if the infection has moved up to the kidneys (pyelonephritis). The presence of dysuria, frequent urination, or cloudy urine can support this diagnosis.
Diverticulitis: Inflammation of the diverticula in the colon can cause lower abdominal pain, usually on the left side, accompanied by fever. This condition is more common in older adults.
Ovarian Cyst or Torsion: In females, a ruptured ovarian cyst or ovarian torsion can cause severe lower abdominal pain and may be accompanied by fever if there's an associated infection.

Ectopic Pregnancy: Although less common, an ectopic pregnancy can present with lower abdominal pain and fever, especially if there's associated bleeding or rupture. This is a medical emergency.
Perforated Viscus: A hole in the wall of the stomach or intestine can lead to peritonitis, an infection of the abdominal cavity, causing severe pain and fever. Prompt surgical intervention is necessary.
Inflammatory Bowel Disease (IBD) Flare: Conditions like Crohn's disease or ulcerative colitis can cause lower abdominal pain and fever during a flare-up.

Endometriosis: While not typically associated with fever, severe endometriosis can cause lower abdominal pain and, in rare cases, may be accompanied by fever if there's an associated infection or abscess.
Tuberculosis: Abdominal tuberculosis can cause lower abdominal pain, fever, and other systemic symptoms. It's more common in areas where TB is prevalent.
Psoas Abscess: An abscess in the psoas muscle can cause lower abdominal or back pain and fever. It's often associated with a history of recent surgery, trauma, or infection.