I see. That’s because you’ve been uploading huge image files (text is unlimited). I checked a couple of your images and they are 3648×2736 pixels, resolution 180 (obviously files straight out of your digital camera). There’s no point doing that: browsers display images at a resolution of 72, and most users’ screens are narrower than 1200px.
One way to solve the problem: you can start using an image editing application to downsize copies of the old images, then edit the old posts, replace the old images with the downsized ones, then go to Media > Library and delete the old images.
Other way to solve the problem: sign up for a new blog, upload images to that blog, insert them to your current blog via URL.