Ovarian Cyst Probs

So, ladies, I am 18 days late for my period. I started having bad pains in my lower abdomen and back pain and couldn't get in with my doctor so I decided to go to the ER. They diagnosed me with a left ovarian cyst. Now the last cyst I had required surgical removal. This one is so far only 2.5cm and seems to be normal. However, I just went to the bathroom and am having this light pink/brownish discharge spotting if that makes sense. So if I start bleeding more, how will I know if it's my period or my cyst that's making me bleed? PLEASE HELP. I have had quite a few cyst before, a couple have ruptured but I never missed my period with one before.