Pain and spotting not at midcycle

Hello:

I'm 25 and have never had kids or gyno problems before. I have had vaginal spotting in my cevical mucous accompanied by a slight, pinching pain on my lower left side for the past few months. The pain sometimes radiates down my left thigh. My gyno told me that it was mid-cycle pain and nothing to worry about. She did a pelvic exam where she found nothing wrong and sent me for pelvic & transvaginal ultrasounds. The ultrasound noted a mild thickening of the endometrium lining, but she wasn't concerned because I was about a week away from my period.

The problem is, I am having the pain/spotting intermittently, not at midcycle. I noticed the spotting gets heavier when I workout (running, cycling). My cycle has been irregular too (between 32-37 days the last few months) and my menstrual cramps have gotten worse in that time - to the point that I feel like I might vomit or pass out). The doctor suggested a polyp and said we should wait and see at my next annual exam.

Anyone else having similar problems or suggestions? I am concerned that my doctor is giving me the run-around.