No line breaks in post paragraphs

When writing a post the press enter twice to space out paragraphs, but when i preview the post, there is no break extra space. It starts on a new line but I need that break between paragraphs for easy ready.

I have read it could be my theme. I do have a custom theme. I have tested using other created themes by others and it works correctly. But in my theme it doesn’t.

What could be causing this in my theme to not have the paragraph breaks?