What can I do to improve my photo captions?

I am a Marine at Fort Meade, Md. I was going to the Defense Information School for Basic Still Photography, I was 3 days away from graduating and was dropped from the course because of my inability to write captions. I am a very expressive writer, and it's hard for me to sum up what is happening in a photograph in 2-3 sentences. In other words I can't dumb things down enough, and when I do it takes me from 30 minutes to an hour to write one that I am satisfied with. I don't know what I can do to to improve my caption writing. I am currently waiting to pick up class, and there's no telling when that will be, but I really need all the help I can get. Thank you