HELP! Stuff underlined that shouldn’t be!

Hi there.

I have a problem with my blog being underlined. Everything, including my titles, text in the side columns, etc. is underlined, starting with the last line of the most recent post. I know HTML code pretty well, and don’t see a code for that in any of my posts. I do not, however, know PHP code.

I am wondering what I did wrong, and how I can fix this. It looks bad. For some reason, this problem is only on my main page (where there are several of the most recent posts). When I go to each post individually, this problem is not there.

Can anyone help me? My blog can be found HERE