My advice would be to stop trying for a while. Stress can hurt dream recall, and chances are that if you stop worrying about it so much for a bit you'll remember one soon enough, or part of one. As soon as you remember any bit of a dream, no matter how small the detail, write it down. Even if it's just a feeling from a dream you had when you woke up (scared, happy, etc.). But don't try to force yourself to remember them right now- that could do more harm than good. Eventually, it will become more natural.