Why does the doctor want to do a colposcopy on me?

I am really nervous about this cause i have had about three pap smears in the past year and a half due to being pregnant and having to move alot. But my recent pap smear came back abnormal and the doctor didn't say much more then that i needed to come in and get a colposcopy done. My main question is would he have me come in and get this done if it just an infection? would i still have to come in a get it done if the abnormal pap smear is ASC-US? Sorry for all of the questions but i want answers before i go into the doctor and this procedure done. I have done some research on the colposcopy already so i know what is going to happen. And i dont think i can have a HPV cause i have been with the same partner since my last pap smear and he has not slept with anyone other then me after all we are married. :) Please and thank you for answering my question. and sorry for the misspelled words.