Formatting Issues with Posts

Hello everyone, I have a problem. No matter what post I write, it always squashes the lines together, even when I insert a paragraph. It also moves the first letter onto the period of the previous sentence. For weeks/months now, I have had to correct every post afterward. There are practically no posts of mine without the “edited” note now, which isn’t that bad. But having to fix every post so it looks somewhat decent is really frustrating. Especially for posts with a lot of text, it requires a lot of extra work. Isn’t there a way to change this?