Here is a secret 
Many native English speakers have issues with poor usage and confidence problems. No writer is alone.
There are grammar tools available both online and as plug-ins that help with English’s often twisted rules and standards and a few of them are free to use.
Also there are different writing tools listed in this thread: Writing tools
It is kept updated and I found a program from that list that I love; there are a lot of options to chose from but these are being used by authors here, so you can get direct feedback if needed.
For the most part, this community is very supportive and will often provide feedback … if practice makes perfect is your motto. (Like @poison_mara getting better every time she writes.)