Anyone or a combination of the following could have happened:

• You applied for credit and was denied
• You made hard credit inquiries (cell phone provider, credit cards, banks, etc.)
• You closed one or more of your old revolving accounts.
• You co-signed for a 3rd party
• One or more of the tradelines are reporting your payment 30 days late

Fir me it was child support info was added to one credit report. My score increased like 50-60 points overnight. I got my free reports and noticed it on one of them. 

I don't know why this isn't discussed more, but 3 years ago my credit score dropped 100 its. and it was because a bad mortgage had fallen off of my credit report after 7 years. I asked a credit consultant why and he said this is not unusual...?