Possible Twitter Hacked Account Help?

[Person L]

I noticed today that I was tweeting ads from my twitter account today and I've never joined anything that would cause me to do that. I changed my password to something much stronger thinking I had been hacked and everything seemed to be okay for a bit. I come back later that night and find I've been logged out of my account even though I didn't log out myself, I type in my new password and find that it isn't working meaning despite changing it someone still has a grasp on my account and changed my password to something else entirely. I reset the password and was able to get back on my account, nothing appears to have changed but I'm worried this will continue to happen even though I changed to a stronger password. Does anyone know what is going on and what I can do about it?

And no don't give me an idiotic answer like 'Twitter suxs, don't use it.' please.