Dear sir,
I have a pain in both side flanks after from 2 day. Please sir tell me causes of pain, and I what to do this. Thank u.

Flanks? That's much too vague. Besides, there is very little chance of anyone knowing the reason for pain in general without an examination of your body and doing some tests, and taking history.
Your kidneys are in the back on both sides, near the outer edges, at and just below your waist. If that sounds like the location, it's a possible reason, but only one of many.

I am not a doctor, nor a professional in this area. But, I would see a doctor if this continues for a few days. I do wish you the best.