I think someone jail-broke my iphone?

Okay so I heard that if someone stole your iphone they can jailbreak it and when you jailbreak your iphone some of the apps stop working. Well I lost my iphone 3 weeks ago and it has a passcode, I lost it at school (library). The librarian said that a student found it lying around and gave it to her. I got it back but some of the apps were not working. When I first lost it I called the first day and it was ringing however for the rest of the week i called it daily and it was closed. So I was wondering did some loser access the data in my phone or not? I'm also really worried because my notes has A LOT of passwords, passcodes, credit card stuff etc. The pictures are not personal or anything but still I don't want someone accessing anything of mine that it private.

If you have a new app called cydia, then it is jailbroken