It is common for the kidney stones to cause flank or lumbar pain. I’ll suggest consulting a urologist for the same and seeking treatment depending on the size of the stone. If the size of the stone is small, it’s usually treated with ESWL in which shock waves are given from outside and stone breaks into small pieces. On the other hand, if the stone is quite big, then the surgical removal of the stone is a better option. Please do continue to drink lots of water for it does facilitate at least in preventing the formation of new stones if not the flushing out of the present stones.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.