I, too, am not very good at this.
Having exact same problem on my blog (category) pages only as well – my main Pages are fine. Best I could figure out after hours of working at this is that it’s related to the positioning of the full posts and the grid (smaller thumbnails). They’re all just being set to sit on top of one another.
I tested and changed my usually right sidebar, and flipped it to the left sidebar layout. This helped a little bit visually, but only in the sense that the grid of my posts is at least not sitting on top of my sidebar. (So if someone’s new to my site, they wouldn’t realize that they can’t see the dozens of posts under the single one showing.) But it still has all of my posts gridded on top of each other like yours, labisca2012.
This happened when I upgraded to wordpress 3.9.2…ironically, I hadn’t updated in almost a year for the specific reason of blowing everything up, but decided to give it a go today. FAIL.
Hope someone can post a style css quick fix or the like soon. I don’t know how to read code to find where we should be overriding the new setting that’s making them stack like this!
http://writingwithchopsticks.com/category/moms-52/
When the page loads, you see what my page is supposed to look like for a brief second before all the posts stack on top of one another…