Hi there.. left flank pain with backpain could be due to kidney or ureter stones. Or ovarian pathology. or left abdomen pain which radiates to back could be due to pancreatic gland infection even.. please get ultrasound abdomen done soon to know the cause.. drink plenty of fluids like tender coconut water, butter milk, fruit juices, keep yourself hydrated well.. if it's kidney stone then depending on size treatment is available. If very small then it passes off just having more fluids, if it's big then removal is needed by surgery.. please consult nearby surgeon soon..