common things being common, you may have a urinary tract infection
, endometriosis, irritable bowel syndrome, depression, lactose intolerance and
many other possibilities. Cancer is close to the last thing I think of at your age (it happens but very, very rarely.)
The only way to know is a good exam, pap smear, check for urinary tract infection, check for pregnancy, check for sexually transmitted diseases, and
blood work to check for anemia.