How to improve writing and composition

I'm in a university course and I've done a few units already which I have passed, the problem i have is writing essays and research papers. This causes me a great deal of anxiety. I want to write and not find it so difficult but how do i do it. People usually say practise writing and you'll get better. That is not always the case, we can write everyday but if it is grammatical incorrect or composition is out of place, what use is that? We are just consolidating on poor expression.

May be I lack the vocabulary or something. I try to read regularly to expose myself to new words and even look up unfamiliar words and it doesn't seem to be paying off. My aim in university is to improve my writing abilities and hopefully if or when I graduate I can express myself well in written and oral format. I don't know How to go about doing this. I am in English speaking country and have gone through primary and highschool here so I don't understand why I struggle through expressing myself. Is it because I lack fully formed ideas, lack of vocabulary, lack of subject matter, lack of writing ability, lack of grammar and composition? Does anyone have any idea how I can improve my writing and composition?