How to force a line break (new paragraph)?

I never had this problem until today. One of my posts looked fine in edit mode. When I submitted it, all line/paragraph breaks were gone & it was just a long run-on sentence (at least it kept my periods and item numbers). I even tried inserting bb code for the breaks and it was hidden but ignored. Are my posting capabilities editable? I noticed HTML and animated gifs are not allowed. Thanks!