The vague pain in the left abdomen and frequent urination may be caused by cystitis, bladder stones, prostatitis, adnexitis and other factors. 1. Cystitis: it may be related to holding urine for too long or prolonged poor hygiene, due to the presence of infection in the bladder, causing damage to the bladder, which will lead to vague pain in the left abdomen as well as frequent urination, accompanied by pain in urination, urgency and other symptoms. 2. Bladder stones: may be secondary to kidney stones, due to the presence of stones in the bladder, repeated irritation of the bladder, which will lead to vague pain in the left abdomen, frequent urination, accompanied by difficulty in urination, pain in urination, hematuria and other symptoms. 3. Prostatitis: men may be related to sedentary, long time hold urine and other factors, can make the prostate gland congestion and edema, can cause the left abdominal pain as well as frequent urination, accompanied by perineal discomfort, urinary incontinence and other symptoms. 4. Adnexitis: If a woman has a vague pain in the left side of the abdomen, increased leukorrhea, urination, consider the left side of the adnexitis with urinary tract infection. There are many reasons why you may have pain in the left side of the abdomen, so we recommend that you consult a doctor for the appropriate examination and treatment.