Positive test then a day or 2 later I’m bleeding

I have had this happen 3 times now. May, September, and currently. I tested positive on Monday, Dec. 2nd, and started spotting Wednesday. The other two times, I spotted and then began actually bleeding. My hcg labs at the dr and never enough to indicate pregnancy. I talked to the nurse yesterday and she basically told me if it picks up go to the er and if it stops to let them know so they can get me in for an ultrasound and labs.

My question is, has anyone else ever had this happen? Is there a reason my hcg would spike for trigger and positive test just to start my cycle? Or am I just broken?