All writers get them. It's the depressing feeling that what you've written is horrible, and, worse, unoriginal. Not only that, but who would ever read what you've written? There are a hundred other authors, already published, who are each a hundred times better at writing than you are. What can you do to combat these feelings of worthlessness? Well, I've found that it helps to just take a break from working on whatever you were writing for a while. Read a lot of good books, and instead of dwelling on how much better they are than you, try to learn from them. Realize that, even if you are never as good as they are, you can always improve. Another thing that really helpls me is just reading back over things I've written a long time ago. It very often surprises me how good some of it is! Some things that I wrote perhaps a year or two ago, and forgot, seem to be pure genius! It's a real morale boost. And of course you can laugh over some of the less-good bits, and say to yourself, "I've really come a long way since writing such a corny/sappy/melodramatic/pathetic piece". Also, pray. Ask God to give you the confidence to go on, to give you good ideas, and above all to use your writing to glorify Him.
Keep writing!
