Why Does One Get Periods Every Work?

I have recently been diagnosed with breast cancer. I am really fine about it. But I have my periods every week!! They last for the same length of time...3-4 days...but are just lighter. Is there any connection? I know that on the 11th I will get my results from the biopsy and remember them saying that they will test for something about hromones...
Please if you could give me some insight I would really appreciate it.
Thank you