WP messing up new paragraphs

Hi. I have an annoying problem with my WP in that it keeps messing up my new paragraphs. Specifically it merges it with the preceding paragraph (without a newline or even a space).

To try to fix it, I go into the HTML and add <p></p> tags where appropriate (i.e. the start and end of a paragraph), but when I save it, WP ignores it and even changes it so that it does that weird thing mentioned above.

It’s a little difficult to describe fully in words, but has anyone else had this or a similar problem? Thanks!