Hi there,
You can see if someone has accessed your account using this method : go to your profile, go to "account related settings" , then under limit IP, there's a link to "Your logged IPs for the last 30 days". If indeed it was someone else, you will be able to see a change in IP used. Surely, then you will have a concrete evidence and mods will be able to help you better. You might wanna also edit your posts which you wanna delete.
Thank you for this tip sir. There really is someone. From Tekirdağ, Turkey. I changed my password as well.