I'm almost having the same problem. I've been trying on and off to LD, probably for about a year now. The only time I have any real success is when I stop trying for a couple of weeks and then I may/may not have a semi-lucid one, but it's really nothing special. Whenever I try to LD, I either sit there thinking too much to try and stay conscious, but then never fall asleep, or relax way too much and go straight to sleep.