Images Within Post Shrink

All of a sudden the images within my posts shrink until they are tiny when my site is viewed in Explorer and on a desktop monitor. I stripped every bit of CSS off my site and am still having the problem. I reset the image size when I inserted the images and that did not help. When I tried one of the wordpress themes (Twenty Fifteen) the images were fine. Any idea what is causing this? Is it a theme issue? Browser issue? Wordpress issue? I may have to change out my theme until I figure it out. Thanks. 2browndawgs.com