I'm not sure what is going on. Which theme did you start with?
It could be you have styled a theme which automatically adds a frame around each image unless you specify the border on each image to be "0"
What I mean is that with images set to "alignnone" (or left), then the text below should all be within the same margin unless the images have frames. You should not have to add space before the text below the images.
As for the line breaks, or lack of them, raincoaster is right. Sometimes switching from the visual editor to html and back will mess up the code for paragraph and lines. And if you work exclusively in the visual editor, your cursor could get between tags without your knowing and then the lines don't break as you expect.
If I were you, I'd look into formating with a little html. Here is a link that might help:
Use divs or p with styling that includes padding for more consistent spacing.
Hope this makes sense?