I have the terrible English grammar?

Hi everyone. I am an Asian American who just immigrate to this country about three years ago. I am currently a high school freshman and I try my best to learn English as my second language. So I can speak English fluently to native English speakers now (but I have accent). I can handle quite well when I listen to the TV, speak to the other English speakers and read the English information(news, stories and anything that is written by native speakers). However, when my teachers in school told me to write an essay or a summary, I really get stuck. I can write a good essay(I am a good writer), but my grammar errors in my essay really hurts and ruin my essay grade. I usually check my grammar when I finished one essay. For me, I just seems like I wrote in the way as other native English speakers, but there are a ton of grammar errors that can be found when my English teacher checking my paper. I really need your guys' help. Does anyone have any idea of what can I do to improve my English grammar? Don't tell me to read the English contexts or whatever the native speakers wrote, it really does not work for me. My grammar errors just emerged when I am writing. You guys can give me any advise or recommend some good grammar improving books to me. If you don't mind, can you please check my grammar of this description that I am writing right now. I will thank you so much if you would like to help me and not mock at me...