Hello! Thank you for the query. Lower left abdominal pain is characteristic for diverticulitis of sigmoid colon. This condition is caused by chronic constipation which you seem to have. Back pain and lower pain can be both also caused by urinary tract infection. Both issues can not be healed with diet. You need diagnostics first. Please consult your doctor, have abdominal ultrasound, blood work and urine analysis. Colonoscopy should be considered. To improve your bowels condition and avoid acid reflux you should avoid fatty foods, spicy foods, alcohol, coffee. Increase fiber rich products, mineral water intake. Start some physical activity. Hope this will help. regards.