You probably need to make short goals and targets. This will enable you to get a sense of accomplishment when these tasks are mastered. Make check lists for yourself, just bullet point notes really. Stop and ask yourself, What is most important and what needs to be done first. Then list all your other tasks behind the first one that you nominated. Try to get some type of a routine happening with your work. When that is established, things that come at you from out of the blue will be easier to handle from being organised from a routine. Observe and listen to experienced people at work. It will give you an idea on how to approach tasks.
Above all keep up your effort. This will be appreciated. One day you will just find everything clicking into place and wonder what on earth the worry was about.

You unfortunately won't always have a boss that is encouraging and promotes a team environment. But try to get through these times, as it is a learning experience in it's self. It will make you a better person and a lot more efficient when you become the boss.