Someone keeps changing my Facebook Password!?

Okay, 3 months before, I logged onto my Facebook and it said someone logged onto my Facebook account in L--something Philadelphia. (The unknown person didn't change my password though) So, I changed it. Then on February 12, 2011, I tried logging on with the same password, it didn't work (No Caps, or Num Lk). So I reset it, when I finished, I scanned everything with Kaspersky Internet Security(Quick Scan, Full Scan, and Object Scans). When it finished scanning at 7:30 A.M. I went to sleep. When I woke up at around 5:00 P.M. I logged into my Facebook account, it said "Sorry, You entered an old password!" I click the button to reset and then I tried logging on my main yahoo (also reset with facebook on saturday too), I entered the correct, new password and it wouldn't let me log in! So I went on my Alternate Email and changed it. Soon, after that I got the email from Facebook, I typed my new password and I couldn't reset it I reached the limit of reseting my facebook password. So I tried logging onto my Facebook account with my old password again, then I looked closely it said I changed it on 2:46 P.M. **I wasn't even awake** on this computer (that I'm using right now, I wasn't even on). After that I tried to log into my Back-Up Facebook account and it didn't work either! I'm now afraid to reset it because I might have a key-logger. **I don't share my computer, None of my relatives that I live with go onto my computer** Help?? What should I do?