How do i check if my content is not uploaded again

You'll need to devise some kind of method to avoid uploading duplicates. I use Lightroom myself, by creating a Publish Service where I store all my submitted files. When they are accepted, I color code them, while leaving the ones still under review the default gray. If they are rejected, I remove them from the Publish Service and keep them in a Category that I call Rejected. I also delete the originals and only keep the finished assets to help assure I don't work on assets that have already been edited and submitted.

If you do not use Lightroom, Bridge might also be an option to keep track of your submitted assets. If you use neither, and use Adobe's drag-and-drop method to submit your images, you'll simply need to create a folder wherein you store all your submitted assets.

Whatever method you use or devise, it's best to start now rather than later. 50 assets are easy to keep track of. When you have a thousand or more, it's not going to get any easier if you haven't come up with a means to keep track of things.