You do sound in a mess! There is no point in carrying on getting yourelf more and more stressed about getting stressed.
Do you not have a tutor, a youth worker, somebody at cadets you can talk to about all this? It sounds to me as if you need to prioritise what is important, make a list and then try and work though your list one at a time. Tell those setting you things what you are doing and ask for their help in creating the priorities, if they are involved they will be more helpful in chasing you for things that were due for them.
What you are describing is something whihc happens all the time in life, and you can only do what you can do. Are there some things you could NOT do, that are unnecessary, you could cut out and make your list shorter.
But do talk to people to get help!