Hi there.. flank pain could be due to kidney or ureter stones. or if it's left abdomen pain could be due to pancreatic gland infection even. If right flank pain then it may be due to gall bladder stones or liver pathology.. 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..