How to find out what derogatory marks are on your credit score

Your credit score is just a number. Your credit report has your entire history of credit that companies use to make your credit score. Once a year you can look at your credit report for free. Freecreditreport.com is popular for this. Credit Karma is another site that will show them to you for free.
You look at them for 2 reasons. One, you can see what is positively and negatively impacting your score. But two, you can send corrections to the credit bureaus if you find mistakes. These corrections will be checked and approved or disapproved. The first time I ever looked at my report, I think I made 4 corrections. There were accounts on there that weren't mine, including a credit card that was opened before I was born. So yeah, they make mistakes and it's on you to keep an eye on it.