Your age makes a great difference in managing your case, but I assure you that these symptoms are not consistent with cancer.
You will need to do some laboratory investigations in order to know the reason of your short periods
and your sore nipples: FSH, LH, TSH, HCG and prolactin
. This is a blood test
and it should be done at day 2 menstruation
Then you should have a pelvic ultrasound
in order to exclude gynecological causes of the back pain you experience.
Of coarse mental stress may cause all this.
Please consult your doctor or send again to see the results of your tests.
I hope I was useful and I wish you good luck.
Dr. Ahmed Bahaa.