Could this be uterine cancer? I got a small cyst on my ovaries and diagnosed with PCOS

Ok, so I was diagnosed with PCOS 5 years ago. I get small cysts on my ovaries and I was getting very bad pimples on my neck. What is wierd is I always have had normal periods. I've had about 4 ultra sounds since being diagnosed to watch the cysts. Let me add I am 30 years old with 3 kids. So this month I started my period on Dec 2 and stopped like normal on Dec 7. We'll 2 days later I started bleeding again. More like a light light period. I've been spotting/bleeding for 13 days now. I've been to the gyno and he ordered ultra sound. I had that done 2 days ago and all they found was small follicle cysts on ovaries ans my uterus linning is 12mm. He noted that for this time of my cycle the 12mm is too thick. He compared it to my last U/S and my linning was 8mm then. So they are doing a biopsy today and I'm super scared. The thickened linning wouldn't scare me if I wasn't bleeding too. Does it sound like I could have early stages of uterine cancer ? My doctor really doesn't semester worried because of my age. But cancer doesn't care about age I believe... I'm so scared :(