I think you're asking quite a lot of someone.
How about posting a fairly short paragraph here and asking for corrections/suggestions and using that as a basis for the rest of the essay??
Another approach is to read it out loud to yourself. Where a phrase or sentence sounds wrong or clumsy, it probably is, and keep repeating/changing it till it sounds 'right'. Take your time, take a deep breath and you'll get there, and don't forget the spellcheck on Word just doesn't correct spelling but also grammar. If you don't have Word, load your essay onto a memory stick and go to your local library. You'll probably have to pay to use one of their computers, but it will be worth it.