18 year old female experiencing mild lower back, lower abdomen, and side pain (especially left side) for over 2 weeks.

Diffuse pain: See a human doc and give him/her a thorough history and detailed physical examination. That is the key to good medicine! You may be asked to have a laboratory exam and imaging (ultrasound or MRI, etc) exams and possibly see a specialist if he's stumped. Hopefully in the words of Frank Mankowicz (in "Casablanca") "This may be the beginning of a beautiful relationship."