Hacked?

A Few Tips:

#1 Don't have the same password for everything.

#2 Change your password often.

#3 For anything Google, you can look at the history. If it's something you didn't search for, then change the password. If it's Youtube, that's easy to check by going to the History tab on the side. You can look at "Last Account Activity" for Gmail as well.

#4 Don't have old/unused accounts opened.

#5 If you get an email saying you signed into an account and you didn't, change the password.