There are several possibilities for what is causing you to have short dreams.

You could be recalling non-REM dreams. These are very short and usually consisit of a repeated image, sound or phrase, or idea. If this is what is going on -- congratulations! Very few people remember this kind of dream.

Maybe you are only remembering dreams from early in the night when the REM phase is shortest. You could be waking up a lot at night. Or instead of having one long dream that is recognizable as one dream per REM phase, you might be having lots of little dream bits per REM phase. Or you could be sleeping too much and using up all of your REM long before you get up.

Think about your sleep and when you wake up at night. When you remember these dreams in the morning does it feel like they just happened, or does it feel like they are from much earlier in the night? This will help you figure out what is going on.

What do you think it is?