duplicate titles

I am told that all my posts have two titles, and a lot of titles are duplicate. I’m using the Twenty Twelve theme. I have only added H2s because the theme already puts H1s.

I don’t know whether this is thought of as an SEO issue so I don’t even know who to ask about it, do I need to hire someone to fix this or do I just need to change themes? Is the theme doing something odd? Yoast may be at the root of this.

Thanks.