What could cause pain on lower left side of stomach?

Broad differential: "LLQ pain" can be caused by lots of things & may indeed originate outside the GI tract. Further evaluation is in order before anyone can answer "what to do." your doctor will want to re-examine you as well as know the quality, timing, duration, location, & associations (eating, position, activity, stooling, urinating) of your pain to better direct the next appropriate testing & treatment.

See below: These symptoms need to be fully and thoroughly evaluated by your physician who can then explain them to you and discuss with you what's best.

See your doctor: Symptoms like these are best deterimed by a thorough evaluation by your physician. Based on his/her findings, a treatment plan can be developed to help you.