I'm assuming English isn't your first language? Don't feel too bad - I see mistakes in native speaker's writings on a daily basis.

See: Simplified Technical English. http://www.asd-ste100.org/ https://en.wikipedia.org/wiki/Simplified_Technical_English

Writing documentation is 100% where the smallest bugs in your english skills come out, whereas speaking allows so much more in the way of context clues to let grammar mistakes slide. It's so tough. If it's any consolation, I have corrected documentation grammar errors from native speakers too

Here in HN I sometimes end up writing several simple sentences instead of a single complex one, because I'm not sure about the grammar, but sometimes that looks awkward.

It worked for Hemingway! My English teachers always advised splitting meandering sentences in half. I have never regretted doing so.