I am having abdominal pain, especially to the lower left of my stomach, it is often worse while lying down, i'm not pregnant, what could it be?

Have it evaluated.: Abdominal pain has numerous causes. See a doctor and have the issue evaluated properly.

Gyn? gi? gu? see MD: Lots of possibilities including: ovarian cyst, twist of ovary ( torsion- surgical urgency), ovulation pain (mittelschmerz), tubal issue including infection, colon/ rectal issues, including inflammation, ureteral stone, nerve, musculoskeletal, other. Tumors, cancers very rare at age 18. See a doc.

Depends: Can be your ovary, can be adhesions, can be musculoskeletal. If the pain is not responding to tylenol (acetaminophen) and is getting worse please go see a doctor.