What Causes Vaginal Spotting Other Than Periods?

Hi, I was due for my period on the 20th of this month. I started spotting on the 21st. It was brown and lasted 4 days. It was very light (actual period didn't come). I went to the drs on the 25th. She said the I wasn't going to have a period since I had eye surgery last month on the 25th. And I should either have spotting again or a really heavy period around the 16th. I started spotting again today. Still not having my period. I do have double uterus and cervix. Can u tell me what's going on?