I'm a little late in replying to this but wanted to offer some advice.
Talk to your tutors, ask for feedback on what you have written, how you can improve it and for any hints and tips they can offer. The same with the staff in the Learning Resources Centre at your uni - there will be someone in there who is able to spend time with you going through essay writing techniques. The course staff want you to pass because failing students reflects badly on them so it's in their best interest to help you as much as they can.
When you get your essays do you get a marking criteria? Our essays were always given to us with the module guide. In this module guide it outlined the headings of what we were studying and therefore what needed to go into our essay or presentation. I used this as a tick list to ensure that I had gotten everything in the essay that needed to go in.
I know a number of the older students on my course all had a hard time with the essay writing, namely because they weren't in the habit of essay writing, it had been a long time for them since studying at school and there's a big difference between school/college and university. So you're certainly not the only one.
I've just finished my degree and have been offered several jobs - none of them have asked for my grades, only that I pass the course to obtain registration with the GSCC.
Hope this helps :-)