First off don't give up!! If your writing a book read some other books that have some good fighting in it to get an idea what to write lol thats what I'm doing. I'm reading Dead City by Joe McKinney. So far there is a lot of zombie fighting in it.
I also recently came across this post on writing action scenes in screenplays. Enjoy!
When I have trouble trying to work out a fight scene, what I find helps me is I physically act it out, this allows you to think about how people would move and react in that situation which can give you a mental image to work off as your writing.
Hope it helps.