Pelvic inflammatory disease is a infection of the pelvic organs that is cause by an STI (sexually transmitted infection.) Sometimes, the only symptom is lower abdominal pain. However, the pain may also be accompanied by fever, chills, vaginal discharge, or abnormal vaginal bleeding. If you are at risk for an STI with multiple sexual partners, have had a STI in the past, have a partner with symptoms, or have unprotected intercourse you should see a health care provider.
This woman asked about lower stomach pain, not lower abdominal pain. If you're having lower stomach pain, do the symptoms get better right after you eat, and then worsen after that? Sometimes that is an indication of an ulcer. If you suspect an ulcer, a little research on reputable websites/ your local academic library and a visit to a nurse practioner or doctor will clear it up.