Pap smear/abnormal cells?!

Here’s the story:

A year and a half ago I went for a routine pap and found out I had abnormal cells so they asked me to come back in 6 months to re-check. Turns out it was fine my pap came back clear. I went back 6 months later as per my doctors request and the results were abnormal cells AGAIN. So this time she is sending me to an obgyn for a Colposcopy. I go next month. My doctor is telling me not to worry, that this is normal and happens to many girls but I can’t help it, I’m so stressed! Can anyone tell me their experience with abnormal cells from papsmears and what happens during and after a Colposcopy? What is worst case and best case scenerio? Also how did my pap go from being abnormal, to normal, to abnormal again?! I’ve been with the same partner this whole time.