Very worried

Hi I'm not sure if this is the right place to post, really sorry if not. 

Since January I've had some mid-cycle bleeding, only a small amount and usually brown. I went to the GP who examined my cervix, said all looked fine (I'm up to date with my smears), and said to come back if it continued. It did continue so I went back and in March I was referred for a pelvic ultrasound which came back normal. After that I didn't really notice bleeding for a couple of months. But now I'm mid cycle yet again and it's back - its blood streaked mucus. Mostly brown but some red. Had yesterday and today. 


Im really scared. Could the scan have missed cancer? I'm 28.