It isn't that you're not dreaming. We dream everynight whether we remember them or not. You're just not remembering them.
Before going to sleep, fall asleep to the mantra "I will remember my dreams". It sounds silly but I do this everynight for a week before asking for questions to be answered through my dreams to make sure I will remember any answers given.
Eventually you will begin remembering bits and pieces. When you wake, don't get up right away. Try not to move at all. People who don't have good dream recall are usually ones who jump out of bed immediately. Think back about that night and go over any dreams or fragments you remember. Once you've consciously gone over anything that was recalled that night, sit up SLOWLY, continuing to concentrate on what you remember. Have a notebook and pen ready at the side of your bed. Write down every detail that you remember. This should be also done if you wake up in the middle of the night too.
Do this everynight for 2 weeks and you'll notice a big difference. Do it for a month and you'll begin remembering full dreams, sometimes even multiple ones depending on how consistent you are with this method.