Is my aim being hacked?

Okay, so here's the deal. I have an AIM, and well, it started Thursday, [April 23rd '09] I was on by my sidekick, so then I took out my sidekick to check my IMs, then I got an AIM, saying something with "your AIM has signed on to another location" which is pretty much saying someone ELSE, is on my AIM. And now it's been doing it a lot. [like right now my sn is online; and i'm not even signed on] BUT here's the thing, at first I thought it was my cousin, but apperantly it wasn't cause she texted me and asked if I was online, and I said no. And well, I asked my cousin to say "hey" to IT on my AIM. Guess what? No Respond, I asked others to IM it too, and again, no response. It's creepy, cause it keeps signing on and off. I'm being hacked? Or What?