Left pelvic pain

I have pain on my lift side below my hip x it started when I had my miscarriage 2 months ago the pain is dull and not there all the time x it's only sore when am on my period x I told the nurse when I was pregnant am on the ultrasound for my scan after my miscarriage she said My uturus was fine x am only 19 and really scared what could this be it scares so much that I cry cos I think it could be something serious