I am 17 years old male. i have kidney stones problem and i am taking medicines for that. but my question is something else. i masturbate once in a week or so. but when i do so i have a severe kind of pain in my anus and anal region?

The perianal pain you have experienced is called referred pain which could originate from prostate, testicles and semimal vesicles. Prostate problem is usually the culprit for pain with ejaculation but you are relatively young for this problem. Due to your history of kidney stones, seminal vesicle calculi should be ruled out. You need to to talk to your urologist, ultrasound can be done.