First off, 3.5-4 hours of sleep is a really bad idea. I mean, it's fine on occasion, but on a regular basis, that is not sustainable. It's going to have adverse effects beyond just lucid dreaming. A prolonged lack of sleep creates a mental state very similar to drunkenness, so you want to stay away from driving if you're going to do that.

I had a semester where I slept anywhere between 4 and 7 hours a night. Averaged around 5. I got through it with a 3.94 GPA, but I was irritable, negative, and on the edge the entire time. If I ever did become lucid, I was so mentally exhausted that I usually allowed myself to fall back into non-lucidity, because I was too tired to even think about what I would do. My brain needed rest.

Dream recall and actually waking up to write in your dream journal are significantly harder when you're sleep deprived. However, the first time I succeeded with WILD was after sleeping about 4 hours, then getting off work and taking a 30 minute nap. So if you absolutely must do that, try and take some naps. It'll help.

But I would really suggest cutting something out to allow for at least 5 hours of sleep a night. If you have to get less than that, then you need to either work more efficiently or scale down a commitment -- like for me, it was cutting working from 15 to 10 hours a week, and only practicing music once a week. You're going to be incredibly exhausted, and it most certainly will have detrimental effects on both your dreaming and waking life.